Thanks for all the advices.
I know good tactics is important but what happens to me sometimes is that after playing for a while, you keep reading stuff and end up learning that you could have made a better build for your character. When this happens, even if I'm doing ok with my current character, I get pissed cuz I know he could have been better. Since I don't usually make a second playtrough, I like having the most optimized toon on my first and only playthrough.