I always hear people complaining about someone outshining the others, but I've never seen that happen. Could someone give me an example of that?
In the game I am currently playing, there is a single-class rogue and a multi-class paladin/champion. At their current levels, the rogue can usually manage to land a sneak attack every round, for about 35 damage. To contrast, the paladin can action surge and smite to deal three or four times that much damage; and it can do so on-command, every single day.
If we're fighting a monster, for example, then the cleric might open up with a Flamestrike, and then the rogue could maneuver for a sneak attack. But then the paladin goes, and it deals so much damage that
not only is the monster vanquished, but it
would have been vanquished anyway, even if the cleric and rogue hadn't done
anything. Two players are left with the sad realization that their contributions toward this shared goal were entirely meaningless, because one player is the only one who
mattered in determining the outcome. That is an example of one player outshining others.
A similar example, from Pathfinder, sees a witch and a sorcerer fighting a group of several ice monsters while they each have a Fireball spell available. The monsters each have about ~80 HP, and the witch goes first with a Fireball that deals ~50 damage to each of them, followed by the sorcerer with a class/race/feat
optimized Fireball for ~90 HP. The witch ends up feeling like a chump, because even though this was an ideal situation to use that spell, their entire contribution and all of the resources they expended amounted to
nothing.
That's just from personal experience, though. YMMV.