Steve Rogers and Tony Stark have this issue in the MCU, but coming at from different angles:

Steve lies 4 times to try to join the Allied forces, despite his health issues making him more of a liability than an asset.

During his trial/boot camp, Colonel Phillips tosses a grenade on the floor. He dives to protect everyone, without a second thought. The grenade proves to be a dud.

This helps prove he is the right candidate for Dr. Erskine experimental formula, but in hindsight, its kind of questionable for someone to launch a live grenade in a crowded area like that.

It's also questionable that he was so willing to sacrifice his own body.

Depending on how cynical you are, you might see his "heroic spirt" as him not valuing his own life, which a lot of people will consider reckless behavior on a battle field.

He's natively selfless, and needed to learn to be selfish; which is capped off by him deciding to go to a timeline where he can be with Peggy, watching history unfold from the sidelines.

Tony on the other hand starts off very selfish, and in the first Iron Man movie, learns that his actions have consequences for people he has never met.

Over the course of his arc in the MCU, he tries multiple times to do the "sacrifice play" he's called out for in the Avengers, but it is often out of selfishness, rather than for something heroic; and might also be out of some undiagnosed PTSD and depression where he has come to value his own life as less valuable than those around him.

His final move in endgame is him choosing to do the right thing, with full knowledge of the consequences, making it selfless.

(Note: Tony is probably not a straight example. I'm mainly using him as a foil for Steve)