The biggest mistake I make is when I'm prototyping something, I usually forget to put
in reply to Stupid mistakes I repeatedly make
at the top. Since over half my prototypes get rm'ed, this usually isn't a problem. But, when a prototype morphs into a real project, I'm not using strict. (!!!) I once had to retrofit 20+ modules in the same project with this "fix".
Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.