|Of course he has an 18 charisma - just ask Juanita and Thelma Lou|
In most fantasy games, characters have ability scores. These scores are rolled by the player and known to the player. This knowledge plays a role in the player's choice of their character's class or career, and it influences their actions in the game.
But what if players did not know their character's ability scores? Might make for an interesting game, no?
(Or maybe a complete disaster)
It all hinges, to use Blood & Treasure as an example, on wisdom. Wisdom deals with awareness, not only of one's surroundings, but of oneself. A character with even average wisdom should be able to gauge how intelligent and charismatic they are ... and how wise they are. The wise man knows what he knows not, so to speak. Characters with low wisdom, on the other hand, assume natural abilities they do not actually have. If wisdom is low enough, they may even be unaware of their physical limitations. A foolish man can talk himself into anything, after all.
Here's the idea - a player rolls his or her ability scores with their eyes closed. The GM writes them down. If you're rolling ability scores in order, all the better. If not, the player can decide which score gets the highest roll, then the next highest, and so on. There will be some clues if you're doing it this way, but no system is perfect.
In all cases, the player does not know his or her character's wisdom score unless it is 13 or higher. If lower than 13, roll a dice - on a 1-3 they think it's average and on a 4-6 they think it is high.
If the character's Wisdom score is 13 or higher, the player gets to know all of her ability scores.
If the character's Wisdom score is 9 or higher, the player gets to know his physical ability scores and either his intelligence or charisma score (his choice). The mystery score is believed to be high.
If the character's Wisdom score is 6 to 8, they get to know their physical ability scores, but not their mental scores. You just tell them that their intelligence and charisma are high and leave it at that, regardless of the actual score.
If the character's Wisdom score is 3 to 5, they don't know any of their ability scores, but are simply told that they are all high, again, regardless of the actual scores.
Now, this creates a certain difficulty, as classes often have ability score requirements for entry. You could tell the player that their character, who they think has a high intelligence, cannot cut it as a magic-user, of course, but then the player should know they have an intelligence lower than 9.
I can think of a couple ways to go with this:
1) If they pick a class for which they cannot qualify, they instead become a wash-out and end up as a fighter or thief (assuming they can qualify for those classes). They might still act like a wizard or priest, but they won't be and they'll know it and probably resent the hell out of those who actually did enter the class of their choice.
2) Another way to go is to permit them entry into the class with lower scores, and apply an XP penalty to their advancement. Maybe a -10% for every score that isn't up to muster. These are characters who try really hard, but it takes them forever to get the hang of things.
The idea here is to produce Barney Fifes in your game - characters who have to get in over their heads a few times before they slowly figure out their limitations. Characters who insist they should try to decipher the magic rune because they have the highest intelligence, even though their intelligence is actually a '6'. Characters who bumble and stumble a bit, just like we do in real life.