People should build each other up, not tear each other down. You will meet discouragers and encouragers in your life. Stick with the encouragers, not the people who tell you what you're dreaming of isn't possible, that the odds are way against you, that you're naïve for even attempting such a thing. These people are dream killers, and if you listen to them long enough, you'll start to believe them, and then you'll give up.
Surround yourself with friends who tell you, "You can do it. Go for it!." Because even if you don't accomplish what you set out to do, at least you gave yourself the opportunity to make it happen. One thing is certain: If you never try, you'll never achieve your goal. If you do try and fail, so what? Try a different approach. You won't have to wonder for the rest of your life, was that possible? Could I have done that?
Did your mom ever tell you, "If you don't have anything nice to say, don't say anything at all?" It's true. Negative words can stop action in its tracks. Positive words can inspire action. Of course there are exceptions. If someone's plans will harm them or cause harm to others, then you have to speak the truth to them, but as much as you can, be an encourager. Strengthen someone's dreams, don't destroy them with discouraging, "It'll never work" words.