[runningskull]

Ugh. This is so misleading. What you really should say is

"do what makes you truly happy for the longest amount of time".

That implies some thinking about the future instead of blindly following something that may lead to short-term but not long-term happiness. Also, it requires that you figure out what makes you truly happy, not just surface-level happy.

It's a lot more difficult to accomplish, but so very much more rewarding.

[weaksauce]

I voted up your comment but the problem with dishing out that kind of advice to a teenager is that there is still a lot of living to do before you realize what it is that will make you happiest.