Another example is just how few simple optimizations I see in code now. Something like

   `while i < someFunction():`

Instead of

   ```
   criteria = someFunction()
   while i < criteria:
   ```

I've seen simple lines like this compound in complexity as someFunction() gets more complex or as the loop increases. There's a billion variations on the idea but I think it is because people aren't thinking about how someFunction() is getting called every iteration. I do think every programmer should have some basic optimization skills just because these types of things would be nonobvious otherwise. Because frankly, this kind of optimization is going to have no real difference in a toy program or even in many isolated test cases but it can easily add meaningful latency to a program. Definitely more egregious examples but just trying to think of something that is extremely low hanging fruit.

The real issue comes when the user is doing things more than just your program...