Why Is “Luck” a Significant Factor in Short-Term Mining Profitability?

Mining is a probabilistic process, essentially a lottery. "Luck" is the term used to describe the short-term deviation from the expected outcome.

In the short term, a pool might find a block much faster (good luck) or much slower (bad luck) than the average block time dictates. This variance directly impacts short-term profitability.

A pool's luck is measured as the ratio of actual shares submitted to the expected shares needed to find a block.