Level Up & OSR Enthusiast
That's how I've usually seen it. As you say, it would be nice to always be thinking of others, but I don't think it's necessary or should be insisted upon by or of the players in your groupThat'd be a nice thing to strive for. Also, maybe deriving enjoyment from the successes/triumphs of other players, could be a good attitude to cultivate - or at least, not completely zoning out when it's not your turn?
It's easy to approach a game like D&D as a cooperative in a sense, but still competitive in others. Like, rivals, each trying to get the most treasure/exp/best items/etc, but cooperating to beat the monsters and generally survive. Heck, that may even be how it was originally "meant" to be played.