Some are born with cognitive advantages, though cutting the grade may be done by anyone average functional through the experience of persistence. Some are instigated by the inspiration of others. Intelligence is contagious.
Cognitive strategies vary so much they are difficult to compare. Good memory vs deduction skills, tenacious will vs opportunistic, dogmatic structure vs chaotic exploration. Quirky yet elegant tastes vs OCD who picks at problems.
Does not regard convention. Beyond aware that there is such a thing, preoccupation of expectations is a barrier. One may not realize they are a smarty pants until long after everyone stalling comments on how far along you've gotten.
Obsession and compulsion has a lot to say for circumstances. Normal people are off enjoying their mental serenity, smarty pants are often agonizing over incongruous abstractions. A smooth character simply does not expose their restlessness.
Not knowing something is enough to stop a normal in their tracks, a smarty will observe, explore, relate, and experiment. Playing around, having interests, and not knowing there were supposed to be limits may be common traits.
Normals are too busy doing something else, comfortable in their not knowing, everything explained away.