Very good point.
> But we don't have the same cultural concern against underthinking. I have never heard someone telling their employee or friend "you're underthinking this". Surely overthinking is bad, but when underthinking can be severely dangerous, it's easy to see why some people overthink.
I believe that it's largely a cultural thing.
For instance, in French companies, US Americans definitely have the reputation of underthinking things (which US employees feel is "being productive"). Reciprocally, in US companies, the French have a reputation for overthinking them (which French employees feel is "assessing risks").
One more reason for which balancing cultures (and backgrounds, etc) is actually really important for the future of a company: we all have different blind spots.