What's a mnemonic or concept that's helped your engineering career?

What are some mental models, mnemonic or memory tricks that you've developed to help you through your software engineering career/journey? I'll start first:

When I'm working in javaScript and trying to figure out whether to use `for...in` vs `for...of` I think about this trick I found and modified (https://maximorlov.com/forof-vs-forin-memory-trick). The author uses UFOs (unidentified flying objects) but I use foreign objects for mine. If I'm looping over objects, I say they are foreign objects so I grab the `for...in` loop for objects. That means the only thing left is `for...of` for arrays.

This other one is less of a mnemonic and more of a concept that was like an "ah-ha" moment in my software engineering career. (I can't remember if I came up with it or read/heard it somewhere so I apologize for not being able to give credit if credit is due.) A large percentage of apps that we create as software engineers are mostly glorified forms and/or spreadsheet. You are submitting some data to a database. We are then outputting that data in some UI. That means everything we do - from design all the way to DevOps - is to support or "dress up" a form and/or a spreadsheet of data. It helped make things a little less daunting for me.

Curious what other's may have conjured up.