Joel Spolsky

think that some of the biggest mistakes people make—even at the highest architectural levels—come from having a weak or broken understanding of a few simple things at the very lowest levels

Whenever something seems like it should have linear performance but it seems to have n-squared performance, look for hidden Shlemiels. They are often hidden by your libraries.

It was the number one cause of hacks and worms in the olden days before Microsoft Outlook made hacking easy enough for teenagers to do