the.com/drop in the bucket

means A quantity so small compared to what's needed that it makes almost no difference at all.

from The phrase traces to biblical language — the Book of Isaiah describes nations as being like 'a drop of a bucket' before God, meaning utterly insignificant by comparison. The image is simple and durable: tip one drop into a full bucket and the water level doesn't even register. English picked up the phrase and kept it largely intact for centuries, a rare case of a scriptural metaphor surviving almost word-for-word into everyday speech.