Ask HN: Example of design flaw that never fade out

Unix/Linux make [0]. As originally written, the rules following a dependency line must be indented by a TAB character. Any other white space causes make to error. Early on, the author was asked to change the program to allow any white space indentation at the beginning of a rule line. The author replied: I had a user population of about a dozen, most of them friends, and I didn't want to screw up my embedded base.

[0] https://en.m.wikipedia.org/wiki/Make_(software)#Rules

Standard keyboards. They're not bad enough to warrant switching everything, so we have to keep living with row stagger inherited from mechanical typewriters, oversized spacebars wasting the most valuable space on the keyboard, etc.

C