WIST

Belief is no substitute for arithmetic.

Henry Spencer (contemp.) Canadian computer scientist
(Attributed)
Cf. "Anecdote is no substitute for arithmatic," cited as a Hebrew Proverb.

Reinventing the wheel is bad not only because it wastes time, but because reinvented wheels are often square. There is an almost irresistible temptation to economize on reinvention time by taking a shortcut to a crude and poorly-thought-out version, which in the long run often turns out to be false economy.

Henry Spencer (contemp.) Canadian computer scientist
(Attributed)
Quoted in E. Raymond, The Art of UNIX Programming, ch. 16 (2004)

Many customs in this life persist because they ease friction and promote productivity as a result of universal agreement, and whether they are precisely the optimal choices is much less important.

Henry Spencer (contemp.) Canadian computer scientist
The Ten Commandments for C Programmers (Annotated Ed.) (1992)