Dreaming of being rich is stupid or too childish?

My Korean friends told me that I've got to think about reality and stop dreaming. I understand what they mean, but I can't agree.

Why do I have to give up my dream and simply "accept" reality and live like everyone else?

If I fail, I think that I might not like the result, but the process would still be valuable to me. Through the failure I can learn things to be successful in future.

But it feels as if I shouldn't be different from them. Like a culture, they push their opinions and their mindset on me that I should live the same way they do.

Am I wrong? Or are they?