Hanlon’s Razor says “Never attribute to malice that which is adequately explained by stupidity.” In other words, don’t jump to conclusions that someone did something bad on purpose when it might have been just because they’re incompetent.
Unfortunately, that’s a bit overly optimistic. Humans are terrible creatures and while a LOT of people are indeed idiots, a lot (possibly even more) are also evil. We need a similar but opposite adage, but it doesn’t look like anybody has made/coined/named one. As usual, I’ll just have to do it myself. Hanlon has a razor and Murphey was a pessimist, so…
Murphey’s Beard: “Don’t assume incompetence when it’s more likely to be intentional”
In some cases, people do bad things because they’re both malicious AND incompetent at the same time. For example, cops are notorious for being purposely harmful but also regularly try to deflect accountability for their crimes by pleading incompetence. Police are in a quantum-superposition of harmful uselessness:
Schrödinger’s Scumbag: “If a human did a bad thing, they’re probably evil AND stupid”