Fiction literature (especially comic books and movies) often includes characters with “superpowers”, abilities intrinsic to them which are beyond that of ordinary people, powers which no humans in the real world have. There are millions of possible superpowers (and some settings, like the X-Men universe, go so far as to include hordes of undeveloped background characters with minor superpowers), but I’d like you to consider just one: Super Breakout Guy, with the power to break out of any confines! No prison holds him, he can always escape. When marooned on a deserted island, the rough and shark-infested waters separating it from the distant mainland don’t block him. Why, he can even escape from more abstract limits: He slips the surly bonds of gravity and takes flight. He sends 200-character tweets. Freedom, heck yeah! He has even broken out of this hypothetical situation and is right here right now!
Well, no. Of course not. Hypothesizing someone able to break out of hypothetical situations doesn’t make them exist. Hypothetically, someone moving from hypothetical to actual would be actual, but actually they remain hypothetical (and that’s no surprise). See this Usenet Oracle post for an especially amusing take on this.
And this is why the Ontological Argument is unpersuasive. It defines God as “being than which no greater can be conceived”, and puts forward for consideration a “being than which no greater can be conceived, and which exists”. Conceptually, this being exists. Hypothetically, Super Breakout Guy is actual. But conceiving something able to become greater than a mere conception has as little power as hypothesizing someone able to break out of hypotheticals: In order to break out of the realm of mere conceptions, such a being must first be admitted to be actual, otherwise it is only conceivable that it could be greater than mere conceptions are.
(What if Super Breakout Guy breaks out of the bounds of logic?)