a fish inside a birdcage

Someone who has all the skills and knowledge to thrive, but due to circumstance, their surroundings, and the people and things their surrounded by, they will likely never live up to their potential. They will often feel inferior and insecure because they don’t seem to fit in, and don’t have the same abilities as their peers. A fish has all the qualities and abilities to survive and thrive, but are helpless out of water, that’s where the saying is supposed to mean on a literal level, but on a figurative level it means someone who has skills and abilities that may be unconventional or less socially acceptable, and are pressured to fit a mold that doesn’t work for them.