Overthinking always helps you take big risks and sometimes you can win by overthinking but sometimes you have to lose a lot. When you overthink, there is a lot of confidence and because of the high level of confidence, big bets are placed. And when you overthink, there is a high possibility of disappointment because when you overthink and place bets with confidence, if that bet loses then you will suffer a lot because you were ready to win at that time and not to lose. Not only in gambling, you should not overthink for anything because it can cause a lot of losses at any time.
You are not wrong, but it's not always an equal result. Most times our overthinking can lead us into big loss, while a few times we could luckily win big because we placed high value on one particular game more than we used to. Since the chances are slim, it's better to reduce the risk by trying as much as possible not to pump in much higher money than the usual staking amount so that if it doesn't work as predicted, the loss won't be that much felt in the person's financial life.
I really wonder how you guys managed to link overthinking with confidence, because to the best of my knowledge, this two has absolutely no connection, overthinking simply destroys concentration, attention and so on, it's not the same as being confident, over thinking is one thing and over confidence is completely another thing, they are both like two major roads that didn't meet or join anywhere.
When we overthink, we lose concentration in what we are doing which could lead to mistakes that some times can be irreparable, take for example one who is trying to place a bet on a football match and at the same time, overthinking about something else, that lack of concentration brought about by too much thinking can cause the gambler to make a mistake which could potentially lead to lose, except he or she still well lucky enough to still end up winning regardless of the errors made.
So in the nutshell, overthinking and confidence have no commonality, both are separate and different in their ways.