Which is why you should spend some time looking at production Every. Day., and following your curiosity where it takes you.
No more.
(Relevant: charity.wtf/2019/09/20/lov…)
I don't care how good your test coverage is; if you aren't watching users use it in prod, you aren't done.
Compound this approach over time and that's how you get a clean, stable system that is well understood. 🌷