We're all in the muck, it's one big party
I think this is best summed up by the Tarot card The Fool
We might be blissfully standing on our mountain top of joy/wisdom/enlightenment/knowledge but there are higher places in the distance we can reach.
To reach them we have to climb down the mountain and enter the valleys. We can't see what's in them, but to get to our destination we have to go through them and climb a new mountain, to reach new peaks, greater heights.
As for why do we keep doing it, for the adventure!