Hope gives effort a reason to remain invested.

Sustained effort requires a believable reason to keep investing, and hope supplies it. Without some expectation that the work will lead somewhere, persistence becomes a matter of willpower alone, which does not last. Hope is what makes long effort feel worth continuing rather than merely endured.

If your motivation is thinning, check whether you still believe the work leads anywhere. If not, either restore the connection or reconsider the work. Grinding on without a reason is a poor arrangement.