do (oneself or someone) an injustice

To do something that hinders or is detrimental to one. You're doing your kids an injustice by catering to their every whim—they need to learn to be independent. You do yourself an injustice when you try to push through your injuries. They need time to heal! There is absolutely a segment of video game enthusiasts who create a hostile and toxic environment online, but you do the community an injustice when you dismiss the whole thing as "toxic."

do yourself/somebody an inˈjustice

judge yourself/somebody unfairly: We may have been doing him an injustice. This work is good.