... and why I think you shouldn't play a character with a higher Intelligence score than you might have.
Many systems have ways of representing a character's intelligence - normally wrapping up things like spatial reasoning, "IQ", and capacity to learn as well. Some systems split these up a bit (like the dreaded GURPS), but for the most part, you can instantly see how "smart" someone is by the number on their sheet.
It's an abstraction we have all come to terms with - even if it doesn't ring true. Look at babies - their ability to learn is ridiculous, picking up things like languages in a few short years that might take an adult a decade. But are they smart? No. Babies are pretty dumb. They have low Intelligence scores, despite their ability to learn at a phenomenal rate.
By the same token, I know people with a massive amount of retention - they can list off obscure facts and figures about their preferred subject, or do gaming-related maths at speeds that make my head hurt. But they have far less in the way of capability to learn and general IQ than such feats would suggest.
Playing a character with superhuman intelligence is hard - as you as a player will make mistakes that they simply wouldn't. Connections that seem obscure and byzantine to you would be a mild strain to such a character - puzzles are simply not, as their brains can piece together the parts in no time at all.
In fiction, it's a mixed bag - I've seen the World's Greatest Minds make amateur mistakes, and fall into a villain's trap with little effort;
"Well, I can calculate Pi to 80,000 places, and recite it in eighteen languages. What's that, supervillain? You have a surprise for me? Boy, I love surprises! What do you mean it's not a puppy? Oh, it's a cage made of my only weakness - now where's my puppy!?"
It's like super-speedsters who use their superspeed to disassemble, fix, and reassemble a car in seconds - but still punch at the same speed as a regular guy (and not at near-light speed). Well, I guess that one's because few superheroes want to vaporise every villain before they've had a chance to get a good monologue off, but you know what I mean.
By the same token, every time I see someone playing (for example) a Wizard, their Intelligence is at or near the 18 mark - baseline human maximum. As in, the smartest 5% of the population fall here. Of course, this is barring edge cases like Stephen Hawking (the man has a Headband of Vast Intellect stashed somewhere in that chair...), but really - gamers are, on average, more intelligent that the average man, but that much more intelligent? I'm not sure.
It just kinda annoys me. Especially when players use the dreaded argument - "But my character wouldn't fall or that, he has such a high Intelligence score!" For me, it breaks the illusion somewhat - but at the same time, it's a game. I really should stop taking myself so damn seriously...