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You Are Better Than You Think You Are, except applied to superpowers.
Also, The Call Knows Where You Live since the mentor takes it upon themselves to give them proper tutelage.
I wouldn't mind failure so much, if I didn't fail so much.
My first thought was Heart Is an Awesome Power, though your situation may lead to this more than be it.
Often the case with a Swiss-Army Superpower, Imagination-Based Superpower, or Semantic Superpower — ie. the power has uses the person hasn't thought of yet. Comes up a lot when the superpowered arms race of My Kung-Fu Is Stronger Than Yours becomes part of the plot, requiring frequent stops for whenever it's Time to Unlock More True Potential again.
Someone has special powers (or occasionally a tool/weapon/etc). Thing is, either:
Then someone else comes to him and says that his abilities have more potentials than he can think of. This other person either is just pointing it out, or actually intends to teach the powered guy.
Do we have this?