Ask HN: Common or important programming compromises

As a beginner-intermediate programmer, I'm starting to get a feeling that a better programmer is someone who is more consistently aware of the consequences of the decisions that they're making when they code. In other words, someone who has reduced their unknown unknowns.

Examples that I've come across personally are knowing the consequences / differences between: An array and a hash table (I come from a non-compsci background, and was exposed very late to hash/dictionary structures); An operational vs a relational database, and when to (de)normalise your data; Using a new language better suited for the job vs the upkeep of adding another language to the codebase.

To the collective experience of HN: what are some common or very importance consequences that you've come across?

P.S. please don't feel limited to technical details. I haven't been exposed to the start-up or internal political side much, but wouldn't mind picking up hints and details