What was the last genealogical item you shared with someone else? It could be some information you discovered, a copy of a record you paid to obtain, a family picture you discovered, etc.?
Sharing is altruistic, but from a genealogy standpoint there is more to it than that. Sharing means “getting it out there” in multiple places and increases the chance that what you share lasts past you. If there’s only one copy of an item (particularly something in paper format), it’s “fragility” is deceased when copies of it are shared with others. Of course the original may still be fragile, but the copies “floating out there” increase the chance that the item is preserved in some format.
Of course when you share, someone else may share something they have with you. That’s an added benefit. But preservation should be high on your priority list.