"Encourage people to do something for its own sake, not for its benefits"

Incentives matter - particularly the right incentives. From Amy Wrzesniewski and Barry Schwartz (NYT):

Whenever a person performs a task well, there are typically both internal and instrumental consequences. A conscientious student learns (internal) and gets good grades (instrumental). A skilled doctor cures patients (internal) and makes a good living (instrumental). But just because activities can have both internal and instrumental consequences does not mean that the people who thrive in these activities have both internal and instrumental motives.

Our study suggests that efforts should be made to structure activities so that instrumental consequences do not become motives.

Personally, I'm of the view that in an ideal world, instrumental consequences reinforce internal consequences. Instrumental consequences can and should, however, guide how you effect internal motivations.