...One of the most important lessons, perhaps, is the fact that SOFTWARE IS HARD. From now on I shall have significantly greater respect for every successful software tool that I encounter. During the past decade I was surprised to learn that the writing of programs for TeX and Metafont proved to be much more difficult than all the other things I had done (like proving theorems or writing books). The creation of good software demand a significiantly higher standard of accuracy than those other things do, and it requires a longer attention span than other intellectual tasks.
Donald KnuthWe should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.
Donald KnuthAlways remember, however, that thereโs usually a simpler and better way to do something than the first way that pops into your head.
Donald Knuth