I wrote some background to this post here. Lots of bits of Greek philosophy have got picked up by Christians over the years, and it takes a long time to get rid of them. One of the bits which is still hanging on in there is the idea that if we're doing something because we enjoy it, then it can't be good.
So, for example, some people think that it's wrong to follow Jesus with the aim of going to heaven.
Compare that with the Biblical attitude:
By faith Moses, when he had grown up, refused to be known as the son of Pharaoh's daughter. He chose to be mistreated along with the people of God rather than to enjoy the pleasures of sin for a short time. He regarded disgrace for the sake of Christ as of greater value than the treasures of Egypt, because he was looking ahead to his reward.
Hebrews 11:24-26, NIV
The key to doing what is right isn't acting against our own interests - it's acting by faith. Faith is recognising that it is more in our interests to follow Jesus than not to.
Then he called the crowd to him along with his disciples and said: "If anyone would come after me, he must deny himself and take up his cross and follow me. For whoever wants to save his life will lose it, but whoever loses his life for me and for the gospel will save it. What good is it for a man to gain the whole world, yet forfeit his soul?
Mark 8:34-36, NIV
A major motivation the Bible gives for being a Christian is consistently self-interest. But it is a self interest that has faith, and sees that the only way to save our lives is to lose them, and that it does us no good to gain the world yet forfeit our souls.
And I know this is very Piper-esque, but that's because he's right on this.