For me it's that feeling when launching; the excitement of expectation. The rest of the day whether I do well or not I will be forever grateful to be able to do something I love whenever, for the most part, I want.
There are days/nights I sit at the helm for a few minutes and take stock in being blessed to do this.
To clarify, of course I want to catch fish but if I ever lose that excitement while launching, the unbridled joy, then I will wonder if it's time.