little frog in a big pond

[little frog in a big pond] or [small frog in a big pond] {n. phr.}An unimportant person in a large group or organization.

In a largecompany, even a fairly successful man is likely to feel like a littlefrog in a big pond.

When Bill transferred to a larger high school,he found himself a small frog in a big pond.

Contrast: BIG FROG IN ASMALL POND.