In the Marvel Universe, Sentry is an example of just how much he fails at that. Sentry possesses the powers of Superman but is also incredibly unstable. Tony Stark has tried to help him, but in one low moment he is outdone by an obscure villain.
Following the massive Secret Invasion event that saw the Skrulls impersonating a number of superheroes, Norman Osborn becomes top cop in America as the director of S.H.I.E.L.D. With the Avengers on the run and in hiding, Osborn sets up his own group of Avengers, which includes Ares, Bullseye, Venom, and the Sentry, who has been manipulated into ing them. Osborn is also in with various villains, one of whom is the gang leader the Hood. Since the Hood has lost his powers, many of his syndicate decide to make a play directly to Osborn and do so in the streets of Manhattan.
One such villain is the C-list mad scientist Jonas Harrow. In 2009's New Avengers #56 by Brian Michael Bendis and Stuart Immonen, Harrow employs a power dampener to neutralize the rogue Avengers while the Wrecking Crew is immune. When Osborn's Avengers eventually show up, the Sentry is first on the scene. Unfortunately, the dampener works on him as well. The souped-up Sentry is turned back into weak Robert Reynolds, who is terrified and has no idea where he wi. Since the Sentry is such a powerful hero, the Wrecking Crew is in complete shock that he has lost his powers like everyone else. In this attack, Harrow has accomplished what Iron Man has been unable to.
This is a huge event in the Marvel Universe as Sentry has been such a liability to the Avengers throughout his tenure. Iron Man, who sees himself as the Avengers' leader, views tech like this as his specialty. He's even vowed on several occasions to either control or stop the Sentry. Iron Man has tried this a number of times when Void starts raging out of control, such as during Norman Osborn's attack on Asgard during Siege or when the new Avengers and the X-Men first try to recruit the Sentry after he breaks out of the Raft.
The fact that Jonas Harrow, a low level villain, is able to develop such a strong power dampener that is able to neutralize the Sentry when Tony Stark can't is a huge representation of Stark's failure. There have been many times when the Sentry has helped the Avengers and been heroic. But if he had a device that he could use to control his powers completely it would not only be a benefit to the Avengers but also might be able to relieve Robert Reynolds's anxiety and phobias. His mental health could be saved knowing there is a way to prevent the Void from returning. Since Iron Man hasn't been able to accomplish that, fans may never know just how great of a hero this Sentry could be.
