If it's just "in the moment", then... I've already had it, and I can't have it all the time. What is there to keep going for?

[If happiness isn't an ending, what is the point of living? He's lived long enough for those moments. Like experiencing sadness to know what being happy is, it works in the opposite way. Can he only go down from here? From the fleeting happy feelings he wants to preserve, when it can't be done? When it can't be permanent?]