originally, i also wanted to add the following, but for some reason in didn't get posted....
i made most of my mistakes in my early college years.... (due to various reasons)... but for some reason, afterwards, i never made the same mistakes again... i think the same holds true for many other things in life...
i think this is much much more complicated than yes/no, depending on implications of mistakes (i.e. you can make a mistake and things still turn out o.k.), severity, how often you make them, etc.
nevertheless, the most important thing is to learn from mistakes, no matter what parameters, IMO
yes, i will now listen to upperclassmen if they tell me to avoid a teacher or a class, because i can't afford to let my grades suffer. I'm only taking classes that are relatively easy (unless it's a pre-med req) and looking at the median score of that class in past years. thankfully, there are enough classes that i like that are relatively fun and easy.
I'm now taking classes that will balance the low grade pre-med classes. so yes, i definitely have learned from my mistakes first year.