In the movie Green Lantern, when Ryan Reynolds goes to the alien planet to get some explanations and training, he is told of the ring's limitations: "The ring's limits are only what you can imagine." He doesn't question this concept, but I do. What if you've got a really active imagination, and you can imagine all kinds of limitations: does that make the ring powerless? And what if you don't have a lot of imagination: does that make the ring all-powerful? So then it follows, doesn't it, that the best candidates to be Green Lanterns would be really thick-skulled, unimaginative meat-heads, so the ring would be all-powerful? Oh, but the great strength of this whole system is that the ring can make anything you imagine into reality, right? So then it would work the best for people with really powerful imaginations. But apparently, that's its only weakness as well. This doesn't make a whole lot of sense. But maybe that's because I have too active of an imagination. (Or maybe what they mean is that the wearer of the Green Lantern ring must focus their imagination on making the ring powerful, and not on imagining limitations that would undermine its powers, so it would be like a self-confidence thing: That might make sense. But that's not what they say.)
Maybe what they mean is that the ring is only limited by the limits of your own imagination, and how the limits of your imagination limit how you use the ring's powers. But then they should have said that. Because what they do say sounds more like they mean that the ring's limits are only what limits you imagine it has. See what I mean? It's just that the way they choose to phrase this exposition is extremely confusing, and it makes it easy to read it as saying something other than what they mean. In fact, I'm just assuming they mean its powers are only bound by the creativity its user's imagination employs to use to ring. But it really sounds like its limits are actively created by one's imagination, as if the limits were created by self-doubt, or paranoia, or subconscious fear, and that's not the same thing at all.
