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

Complexity control is the central problem of writing software in the real world

The only way to write complex software that won't fall on its face is to hold its global complexity down - to build it out of simple pieces connected by well-defined interfaces, so that most problems are local and you can have some hope of fixing or optimizing a part without breaking the whole

Treating your users as co-developers is your least-hassle route to rapid code improvement and effective debugging.

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

It is widely grokked that cats have the hacker nature

Any tool should be useful in the expected way, but a truly great tool lends itself to uses you never expected.