Have you ever guested in somebody else's long-running campaign? If so you might have come across a referee who indulges one player over the rest of the table. It doesn't occur in every gaming group, and if it happens in your own regular sessions you probably haven't noticed it. But here are some warning signs...
When you were setting up your campaign, did a player come to you with a shopping list of special off-the-book character buffs? "Can I have immunity to everything? 5 points would be a reasonable cost, wouldn't it?" If you granted those, then face it: that player is your teacher's pet.
There's also the case of the player who is aware of the kind of thing his or her referee likes and so plays up to it. "I swing on the chandelier, soar nimbly across the shoulders of the guards and somersault to land in a crouch before the princess." If the referee applauds ("Oh, beautifully done!") when they'd ask anyone else for a dice roll then the player is probably a favourite who knows the referee's fondness for swashbucklers. A newcomer to the group, unaware of the codes that unlock referee approval, would have to work that much harder.
I don't think the solution is to bake everyone's fifteen minutes into the rules. That just forces the game to follow the patterns of a bad TV show: "So I can't shoot this guy, despite being MI6's top assassin, because I already had a couple of highlight moments earlier in the session..?" But you do need to monitor who is demanding the lion's share of your attention, and whether the quieter players are happy about that. If they're not, make sure there are opportunities for them to shine too. Otherwise the first sign of that gathering resentment might be when they stop turning up to the game.