And if you've typed in l when you should've 1 typed a 1, or a 1 when you should've typed an l, you're likely to miss it. If you've made a mistake with upper and lower case. Things like that. So just be very careful looking at that.

如果你本来想打，1，的时候,却输成了，l，或者打，l，的时候输成了，你很可能注意不到这个错误,如果你把大小写弄混了也是一样,要注意这个错误。

麻省理工公开课 - 计算机科学及编程导论课程节选