On guessing

“Does not matter how smart you are, if a guess cannot be backed up by experimental evidence, it is just a guess.” – Richard Feynman

On theory

“It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.” – Richard P. Feynman

Optimisation

Don’t be too quick to optimize code for computers, human beings experience pain, computers don’t.