How do you know when your mind is /too/ complex and you're
overanalyzing the problem?
You don't. However, as others are fond of saying, I'm the result of
millions of years of trail-and-error evolution and that does mean I'm
equipped with a host of really good, tried and true heusteristic tools
that makes my mind `complex enough.' That we're here at all is likely
proof enough in the general sense.
Note that just being rational doesn't guarantee you won't make
mistakes. It just means you're more likely to believe your flawed
axiom until too late.