I don't like this one, either:
If you volunteer to join a superteam, the hero with the power most similar to yours will leave for some reason, and you'll have to replace them. Not because you're evil and planned it, but just because that's how fate has it.
For example:
I can generate force fields. I volunteer to join the Fantastic Four. Who do you think will need a replacement that day?

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"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song