Why Are Shares Considered “Proof-of-Work” Even Though They Don’t Solve the Block?

Shares are considered proof-of-work because they demonstrate that the miner has performed the necessary computational effort (hashing) to find a hash below the pool's set difficulty target. This process is identical to finding a block, only the difficulty threshold is lower.

The pool accepts this as verifiable evidence of the miner's contribution to the collective effort.