18. An interface whose human factors are well considered, but looks like butt, still trumps an interface that looks slick but is terrible to use. An interface that is well considered AND looks good trumps both, and is perceived by users to work better than the same exact interface with an ugly design.
19. Don't force the user to remember things if you can help it. Humans are really bad at remembering things. This includes passwords, sms codes, sums, function names, and so on. My own personal philosophy is to consider humans a part of your system, and design around our shortcomings instead of thinking of users as adversaries. Software should serve humans, humans shouldn't serve software.