Bob is a psychic. He can generate telekinetic barriers, and he's also a telepath. He just can't do both at the same time.
Somehow, a character is not able to use two of his superpowers at the same time. Maybe they share the same energy source and its strenght can't be divided to be used on both powers. Maybe they never learnt how to do that. Or it can just be handwaved. They just can't do it, at least for now.
- Jesse Custer from Preacher was able to beat his former friend Cassidy, a super strong and super fast vampire, because as was stated by Custer, Cassidy didn't know how to put his strenght and speed together.
- Variation: Mimic, from Exiles, could replicate Colossus metalic form, but he became immune to telepathy whenever he did that.
- Emma Frost, from X-Men, developed a secondary mutation that made her able to turn her body into diamond, but she couldn't use her telepathy while transformed.
- Blaastar is a Marvel villain who can shoot energy blasts from his hands. He also can fly powered by the same energy blasts, so he can't attack with them while flying. As he is Nigh Invulnerable, he's still very dangerous as he rams himself against his foes.
- On Smallville first seasons, the Monster of the Week use to be small fries that Clark should be able to wipe the floor with... but he doesn't has practice with combining his super strenght and super speed, so they are able to be decent challenges. On later seasons, as The Blur, Clark's modus operandi is solving crimes while using his super speed to become almost invisible, overcoming this trope.