In what ways does hard work make you feel fulfilled?
Work involves moving a force through a distance. Hard work means moving a large force a long way. So why does concentration exhaust us? The brain is a big user of energy and so depletes or reserves. We feel tired, not fulfilled. We feel fulfilled when something goes right. The effort involved or the energy converted is irrelevant.
So work and fulfilment are not connected.
Only politicians and bosses think work is fulfilment.

For the rest of us, listening to your kids playing the piano, or kicking a ball around, is fulfilment. You go to work, to pay the bills to enable the good, fulfilling things in life to happen.
Don’t get confused by capitalist rhetoric. They want the last drop of blood from you so your kids think that’s how it should be.
Work life balance!
Demand it!
They can’t sack us all.