It means that the circle this person is in is too small and cannot reflect the value of this person. The implicit meaning is to let this person change jobs or work somewhere with more room for advancement.

The fish here refers to this person, and the pond is a metaphor for the circle in which this person works. There is a huge fish in a small pond, and this fish will feel restrained. The same is true for this person. There is no room for the fish to continue to grow larger, which is a constraint for the fish. Extended information

A person should be a big fish in a big pond:

A big fish in a big pondgt; A big fish in a small pondgt; A small fish in a big pondgt; Small fish.

The weak have a chance to counterattack, but they must not take the usual path, and they must understand the pitfalls on the road and work hard to avoid them. Regarding the part about not taking the usual path, Nietzsche made it very clear centuries ago. In order for the weak to defeat the strong, they must break through the rules of the strong and not play according to common sense.

Later, the French poet Gépont wrote, "You can't get out of the tree by walking through the tree." I like it very much. One sentence is worth a thousand words. In contrast, Gladwell's books are very average in both connotation and expression, and can only be read in a fast-food way.