[whateveracct]

occasionally but usually not

the reasoning is about correctness and program behavior

Haskell is still the only mainstream language that truly delivers on "understand the part without needing to consider the whole." Others can with work and discipline. With Haskell, you usually have to work hard to get in that level of quagmire (and I've seen and fixed plenty of quagmires. I've seen people complain about code too and just be wrong when I got my hands dirty for like an afternoon.)