Missing the single most important thing, that people seemingly are purposefully trying to avoid nowadays for some reason:

- It depends

No solution I've come across, is a solution for everything, everywhere. It's almost always context dependent, and something that is right in one place, can be utterly wrong in another, and there is no universal truths regarding design and architecture.

The more flexible you can be with "right tool for the right job", the easier time you'll have designing, because you're no longer trying to shoehorn in things that are "right" and "correct".

> - You should spend more time thinking about naming things correctly.

This should almost be on the list twice too, the amount of people who couldn't care less about naming, is so damn high, but if people just cared a tiny bit, it'd solve so much future confusion. Whenever I get pulled into helping a "legacy project" or whatever, establishing a "true vocabulary" based on what people actually call things, is the very first thing to do, because it always uncovers that people been talking about different things the entire time.