When someone asks, "What do you want to be when you grow up?", a lot of people answer that they want to be happy. But happiness is not something you can plan. Everybody wants to be happy in the future, but happiness isn't a concept you can put to the side and say you'll achieve later. There is no definition of happiness, there is no key to happiness, and there is no time frame for happiness. Happiness is whatever you want to turn a moment into.
Next time you don't do well on an exam and think you're not going to do well in the class and therefore not going to have a good GPA and not going to be able to get the job you want and never be happy, stop yourself. That's what it means to postpone happiness for the future. You need to design happiness for the present.
Take a look around you. You're surrounded by friends who care about you, memories you'll never forget, opportunities you never would have thought to be imaginable, and who knows, maybe you're even standing under some really pretty stars! Turn that into happiness.
Don't let the risk of the future blind you from the present right before your eyes. The future is in the future for a reason. Be happy for where you are now.