To my dear friends who speak English:
This essay was originally written in Chinese and translated to English. "Translation" not only means encoding thoughts with different characters, but also means that the original context was in China, or even limited to a few people I know in China; therefore, some presumptions might not make sense in an English-based culture.
Chinese phrases are all marked by Italics for your convenience. Some of them do not have an official translation. I translated them by myself but, in limited time to work on this, there could be mistakes, loss of meanings, and awkward Chinglish, please forgive that.
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在开始谈论二十岁生日前，我认为有必要先议论一番，重视二十岁生日的意义是什么。
法定的成年人年龄是十八岁以上，在美国则要到二十一岁才允许饮酒，这些法律（大概）体现了现阶段所知大脑完全发育的年龄。如果按照常规的进度上学，十八岁高中毕业，二十二岁大学毕业，如果将这个时间视为人生的转折点自有道理。只有上两年制大学的人才会在二十岁左右面临真正意义上的转变，但除此之外庆祝二十岁的人照样数不胜数。我们纷纷调侃“二十岁老年人”、“开始奔三”的时候，其中的特殊性是什么？为什么庆祝二十岁，而不是19.5岁或20.5岁？
这其实是再简单不过的道理——二十这个数字的特殊，是基于我们普遍使用的十进制。
你看，20这个数字完全由2和5的乘积组成。任何数被它相除，最多会留下清爽的以五结尾的两位小数（找零钱也很方便），不会有剪不断理还乱的无穷小数；任何数与它相乘，也非常便于口算，用不着特地从手机中调出计算器。所以比起二十三这种质数，我们当然更喜欢二十。
我们在语言中惯常使用“二十几岁”这样的说法，把二十岁和接近三十的二十九岁并称为同类，自然就有奔三的说法了。虽然严格意义上说，只要年龄小于三十，那每一天都比前一天更接近三十岁；2018年出生，现在还嗷嗷待哺的小婴儿们其实也符合“九零后”，也就是“诞生时间在1990年及以后”的定义，但社会的约定俗成是用“九零后”这个词专门指代1990-1999年，甚至比“九五后”更侧重1995年以前出生的人口。想想看，假设我们的社会习惯用八进制而不是十进制，那可能从十七岁开始就要“奔三”，对年龄、年代的印象也会非常不一样。
我们一年的时长约是365天。虽然表面上看起来也是一个还不算复杂的5的倍数，但实际上365是奇数，又不是3的倍数，不太容易分割成二等分或者三等分，也就没办法选定一个天数。所以婴儿有庆祝诞生百日之说，却少有半年庆生之习惯。当然也可以说上一个生日之后的第182天的正午是182.5天即半年，但按照这个逻辑，整数的生日就必须在午夜才是整好的时间，也不太方便。可以说，这个数字正正好好的程度，和20比起来差得远了。
Before starting to talk about my twentieth birthday, I think it is necessary to make an argument on why the twentieth birthday is important.
The legal threshold of adult is 18, and legal drinking age in US is 21; these laws (probably) demonstrates our current understanding of complete brain growth. If one goes to school at regular pace, she would graduate from high school around 18 and graduate from university around 22, which are considerable turning points of life. Only those who enter community colleges might face significant changes at 20, but countless people still celebrates their twentieth birthdays. What is special when we joke on "an elder in his twenties", "start to approach thirties"? Why 20th birthday, not 19.5th or 20.5th?
The idea can't be more simple -- the specialty of number 20 is founded upon our decimal.
You see, the number 20 is solely made of product of 2 and 5. Any integer divided by 20 results in two-digit decimals ending with 5 at most complexity (giving change also becomes easy), and messy infinite decimals would never be produced; the product of 20 and any number is simple enough to calculate without finding calculator from cellphone. Of course we would prefer 20 over prime numbers like 23.
"Twenties" in our speech puts 20 years old and 29 years old into the same category, so what follows is the term "approaching thirties". Strictly speaking, anyone of less than 30 years old is closer to 30 at the coming of each new day; the little infants born in 2018 are in accordance with the definition of "post-90s" as "born during or after 1990", but the common practice only refers to those born between 1990-1999, even emphasizing more on the period before 1995 in contrast with "post-95s". Think about it: if the society uses octal instead of decimal, we would "approach thirties" at 17, and our impression on age and era would be very different.
One year is approximately 365 days. This number as a multiple of 5 appears not so complicate, but 365 is an odd number and not a multiple of 3, making it less easy to divide into 2 or 3 or select a date in the middle. Thus babies celebrate their 100th day, while half year birthday ceremony is rare. We could alternatively choose the noon of the 182th day after birthday as 182.5 days or half a year; yet if we really buy this logic, regular birthday must happen in midnight to guarantee a whole number day, which is inconvenient. As a conclusion, 365 is far less integral than 20.
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既然论证了2、5倍数的优越性，关于二十岁生日的纪念就应该以近两年、五年、十年为单位，或者以两岁、五岁、十岁至今作为总结的时间点。不过就算搬出数年前的幼稚言行以证明如今的成长，也只会感到尴尬。实际上，写一篇公正的历史是不可能的。
人类只能活在一个又一个的当下。假如二十岁生日提前一个月到来，我完全可能因为心境的差别对人生产生截然不同的反思。有时我觉得生不逢时，大势已去，除了重启人生以外别无他法活好了；有时又感到努力充满价值，每一天都在迈向更光明的未来。同样的一起事件便会因当下的心情产生相反的解读；换言之，任何经历都不存在客观的好坏。
这样一想，每隔365天反思一遍自己的诞生，其实是对生活状态的抽样调查——既然经历不存在好坏，那么就可以将反思本身留存档案，用于日后分析此时的生活质量。但以生日为时间点的抽样一定会有所偏差，因为“庆生”会放大个人之于社会的存在感与庆祝仪式所带来的短暂幸福感，比平常更倾向于乐观。故而生日既是最适合反思的日子，也是最不适合反思的日子，就是这样古怪的结论。
Now that the superiority of 2 and 5 multiple is shown, the memorial essay about twentieth birthday should give a throwback by 2, 5, 10 years, or by the time since 2, 5, or 10 years old. Though bringing out childish anecdotes from a few years ago to contrast personal growth only feels awkward. Actually, writing an unbiased personal history is impossible.
People only live under one present moment after another. If my birthday comes a month in advance, I could have a completely different reflection of life due to shifts of mood. Sometimes I find myself born in a wrong time, opportunities have slipped away, and life can never become better except restarting a new one; in other time I find all diligence pay off, and every day leads towards a brighter future. One same event can have opposite interpretations depending on feelings at present moment; in other words, any experience cannot be evaluated objectively.
What follows is, reflecting on my birth every 365 days is a sampling of living status. Since experience cannot be objectively good or bad, we can document the reflection itself, which can be later used to analyze the quality of life in this period. However, sampling on birthdays is inherently biased, because birthday celebration aggrandizes individual's importance with respect to society and ephemeral happiness, resulting in inclined optimism. Therefore, we arrive at the bizarre conclusion that birthday is the best day to reflect and the worst day to reflect.
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庆生的虚伪正如对着蛋糕蜡烛许愿“想要时间”而不可得。应该像骨髓捐献书上的条款那样为社交网络的一键祝福与企业短信的运营商做注脚，“请认识到自己的责任，切勿给患者带来虚假的希望”。我试图将重心从二十岁这个时间点转移向过生日的个人，却发现个人的价值亦是有限的。对你来说，从不认识我转为认识我的过程的能量差，远远大于我在与你无关的地方慢慢长大的能量差；对我来说，社会潮流塑造个人的引力之大，很少留下发展个性的余地。我这个个体还算健康地活了一小会儿这件事实，没什么特别。能活着本来就是物质条件的恩赐。
The falsehood of birthday celebration is like wishing "I want time" at birthday cake candles but not really obtaining it. The "send a greeting" buttons on social media and commercial message providers should include a footnote like those in marrow donor registration forms, "think very carefully about your commitment ... [do not] give false hope to patients." I hope to shift the focus from the 20-year timestamp to the individual, but discover that individual's value is also limited. From your perspective, the energy radiance in the process from not knowing me to knowing me is far greater than the energy radiance when I slowly grew up at somewhere you don't know; from my perspective, the gravity of the mainstream shapes individuals so much that it leaves little space for personality. The fact that I as an individual of human species survived for a while is nothing noteworthy. Our survival is the gift of overall material wealth.
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也许你已经发现上文自相冲突，并且质疑其可信度。
你怎么知道这些文字是同一人所思所想呢？他们是不同的。写下这句话的是19.96岁的我。潜意识里信奉歪理的是另一个我。一个我睡在家中的橱柜，一个我向台下的观众示以微笑。网络中虚拟的我。网络中另一个虚拟的我。在上世纪出生的我。在宇宙尽头六道轮回的我。梦中的我。在你心目中的我。在我脑壳里的我。
还有更多的我已经死了。在某月悲伤无比的我死了。在某天讴歌生活的我死了。我在我忘记_________的时候死了。我在_______退出历史的舞台的时候死了。我在选择____的时候死了。我在另一个我活下去的时刻死了。
你看到无数个我的遗迹，能追问的却只有当下的一个我，而我只能回答“不知道”。
You probably have already found out contradictions from the texts above and question their credibility.
How do you assume that these thoughts and ideas come from one coherent person? They were different. There was an I at 19.96 years old writing down this sentence. There is another I worshipping sophistry in subconsciousness. An I sleeping in wardrobe in home, an I smiling at audiences under stage. A fictional I on Internet. Another fictional I on Internet. An I born in last century. An I reincarnating at the end of universe. I in my dream. I in your mind. I in my shell.
More of I have died. The I in misery in some month has died. The I eulogizing reality on some day has died. I died when I forget _________. I died when _______ ceases to matter in history. I died when I chose ____. I died when another I could continue to live.
You see the traces of infinitely many me, but the only one you could ask is the one me at the present, who only answers "I don't know".
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把连续性的问题扔到一边去吧。
能全心全意地活在当下是最美好的。构成“我”的定义的是我现在正在做的事情，不是曾经做过又早已放弃的事情，也不是活成正经人的可能性。二十年以来怎样，二十年以后怎样，根本就无所谓——这确是我此时此刻的心情。
这是昙花一现的珍贵时刻，就算历史能快进或倒退，也不会再度出现。
或许在下一个十年、二十年回首的时候，我会感到现今的一切选择愚蠢透顶。那时候我说不定成为了一个比现在更博学多识，对社会做出过更多贡献的人，我发自内心期待那一天的到来。
Throw away problems with continuity.
Being able to live full-heartedly at present is the most wonderful thing. What defines "me" is what I'm doing right now, not what I once did but already gave up, not the potential to live like a serious person. The twenty years gone, the twenty years coming, none of those matter at all -- I indeed believe so right now.
Looking back after the next ten or twenty years, maybe I will find my every single choice now strikingly stupid. At that time I might become a person more knowledgeable and contributing more to the society. I sincerely look forward to the coming of the day.
=== 感谢阅读 / Thank you for reading ===
退屈な世界 これからも一緒だよ