Are your goals life-changing? If you sell your current startup successfully, what would you do afterwards? Start the next one? Basically the same daily routine? Congratulations you are already happy. Maybe you didn't know that.
Even though I would classify my state as 'happy' now doesn't mean that I'm not tempted to think something else would enhance that happiness though. That's the challenge.
A lot of us are ambitious people, driven by the need to out-perform ourselves and build something better. It is then natural to think that you will be better off once you reach that goal compared to how you are right now. The important thing to realize is that more than the goal itself, it's the journey that we tend to enjoy. Once you realize this, having ambitions and seeing a clear path to reaching them is itself joyous.