Confidence is the alief that you have high value, and it induces confidence-signalling behaviors. People judge your value partly by actually looking at your value, but they also take the shortcut of just directly looking at whether you display those signals. So you can artificially inflate your status by having incorrect confidence, i.e. alieving that you're more valuable than you really are. This is called hubris, and when people realize you're doing it they reduce their valuation of you to compensate. (Or sometimes they flip that modus tollens into a modus ponens, and you become a cult leader. So it's polarizing.)

But it is a prosocial lie that you should have incorrect underconfidence, i.e. that you should alieve that you have lower value than you actually do. This is called humility, and it's prosocial because it allows the rest of society to exploit you, taking more value from you than they're actually paying for. Since it's prosocial, society paints humility as a virtue, and practically all media, religious doctrine, fiction, etc. repeatedly insists that humility (and good morals in general) will somehow cause you to win in the end. You have to really search to find media where the evil, confident guys actually crush the good guys. So if this stuff has successfully indoctrinated you (and if you're a nerd, it probably has), then you should adjust your confidence upwards to compensate, and this will feel like hubris relative to what society encourages.

Also, high confidence has lower drawbacks nowadays than what our hindbrains were built to expect. People share less background, so it's pretty easy to reinvent yourself. You don't know people for as long, so you have less time for people to get tired of your overconfidence. You're less likely to get literally killed for challenging the wrong people. So a level of confidence which is optimal in the modern world will feel excessive to your hindbrain.