Have you had people tell you something's not possible or that it's extremely hard and be generally condescending?

I've had a handful people say that to me when it comes to my ambitions. I mean I know it's not easy but people do it so why should I just not even try? Is it jealousy and not wanting other people to get ahead? Or because they themselves were too scared to try?

Anyway, I do end up always proving them wrong. So experience has told me those people have ulterior motives and aren't giving sincere advice.