Why does "don't overthink it" usually come up in situations that actually needed thinking?

I have noticed this in really small and everyday situations like nothing big happens. It's just a tone, a comment, the way smth is said or handled that feels a little off in the moment like not enough to react to immediately because it would feel like making smth out of nothing. So we just let it pass and keep things normal and if you even try to bring it up it quickly turns into "you are overthinking it" or "it's not that deep" and for this you drop it. Well partly because it's hard to explain why it felt off in that exact moment and partly because you don't want to drag something small into a bigger conversation but later when you think about it properly it still doesn't sit right and then you realise it's not even about that one situation......it's how often this exact pattern repeats where smth feels off, gets brushed aside and you end up questioning your own reaction more than what actually happened all