What is logic behind this?

Can someone's words really alter the fate of someone like those curses used by Rishis in scripture and if it is true, what's the meaning of karma? If someone does good karma in this life why does he have to suffer for the karma he did in a previous life by that body which is already destroyed? One more question this one is stupid, today I heard Mom and Dad talking about my results as I failed my previous 2 CA attempts, so my dad was telling Mom that it is hard for someone like me to be successful and that I am not good enough for CA and i am a failure. I was chanting My lords name to divert my mind but a thought came to my mind like "Aap chaho waisa ho" i didn't intend to think that but like a intrusive thought it came to my mind. Can this affect my career?