The Psychology of Probabilities

In a conversation regarding saving throws I had, someone argued that magic users had better saving throws versus spells than the other character classes, hence it wasn't worth attempting to cast a Light spell on their eyes.  When you work out the numbers, though, a level 1-5 magic user has only a 35% chance of saving and a 6-10 level magic user still has less than 50-50 odds.  When you throw initiative into the mix, the chance of coming out on top is better, but it's by no means decisive.  Since we're gambling, D&D is, after all, governed by chance, I'd say cast the spell on a spell caster.  They may do better than average at saving but it's still not great.

That left me wondering about the psychology of probability.  It seemed like the fact that a character had better than average odds of success was taken to mean that they had good odds of success, which isn't the same thing.  I guess it revolves around what you mean by "good."  "Good" in this case is a relative term.  One must always ask "good compared to what?"  If they mean other characters, then yes, magic users have good saving throws versus spells.  The thing is, what really matters is not the other characters.  A probability is a number between 0 and 1.  With 0 meaning I'd bet I'll never happen, and 1 meaning I'd bet it'll always happen.  Ideally, when one makes decisions, it'd be with only the 0-1 scale in mind for assessing their risk of failure.  In practice, though, this person seemed to reveal that what really matter is other people's risk of failure. 

It seems like a statistical version of keeping up with the Jones'.  As as if people aren't going to do something because objectively they'll do well.  They're going to do something because they're more likely to better than they other guy.