One point I’d like to add which a lot of people disagree with is that we should all focus on writing simple and easy to understand code. Enigineers shouldn’t worry too much about optimizing code unles there is a good reason to do so.

I’d say about 1% of my code has ever required me to return and optimize it.(I usually write apis that are utilized by end user apis). Most of the time my code is more than fast enough and user concerns are more around bugs related to requirements.

In the few cases I have had to optimize its usually been a super obvious problem. For instance there was a Scala API that looped over a list of lists and called the Scala built in find function. That function is linear and incredibly slow I just converted the first list into a hashmap took a call that took 30 seconds to under 3 seconds still slow but order of magnitudes faster. It’s usually been silly stuff like that.

All of this of course depends on the domain you are working in some applications require you to squeeze out every millisecond in which case most of this won’t apply to you.