https://superuser.com/questions/1104212/why-do-serial-ports-send-data-least-significant-bit-first
其实是没有什么强制性的理由的，单纯是一种历史习惯。
Well, the reason why is that the engineers that designed the first telex system a century ago thought that was best. And, if you ever study the insides of one of those ancient machines that translate serial data into actual printed copy with no electronic, only mechanical, devices; you may realize what their thoughts may have been.