Because the world told you to? Because not everything worked out the exact way you planned it the first time? Because people convinced you that dreams were for children and idiots?
Ignore that noise. The audible world is full of grown babies crying because they did not get all the toys they wanted. Don’t listen to them. Listen to your own voice instead. It always knew you better than any of those naysayers anyhow.
Dream. Even better than that: dream big. Then, be brave and work your way to a glorious life.