A critical factor in its success was that the X developers were willing to give the sources away for free in accordance with the hacker ethic, and able to distribute them over the Internet.

Rushing to optimize before the bottlenecks are known may be the only error to have ruined more designs than feature creep. From tortured code to incomprehensible data layouts, the results of obsessing about speed or memory or disk usage at the expense of transparency and simplicity are everywhere. They spawn innumerable bugs and cost millions of man-hours - often, just to get marginal gains in the use of some resource much less expensive than debugging time

Given enough eyeballs, all bugs are shallow (e.g., given a large enough beta-tester and co-developer base, almost every problem will be characterized quickly and the fix obvious to someone).

A security system is only as secure as its secret. Beware of pseudo-secrets.

The easiest programs to use are those which demand the least new learning from the user

Of course, C proved indispensible to the developers of all its alternatives. Dig down through enough implementation layers under any of the other languages surveyed here and you will find a core implemented in pure, portable C

When your language is nowhere near Turing-complete, syntactic sugar can be your friend.