In theory? Always. In practice? Virtually never.
The older I get, the more I realize Ayn Rand was onto something with her virtue of selfishness theory. No one does anything, even altrustic, that does not benefit them in some way, even if it is just the warm fuzzies one gets from being charitable.
The trick is--and this is specifically what I have learned from the experience of aging--is to not be negative about motivations. Conceit is a part of life. Just be glad it works out for the best from time to time.