Every Olympic athlete works toward the goal of winning. They want that gold medal. Yes, some athletes play for fun and others play for community, but even those are rewards to be gained. The truth is, humans rarely do anything for no reason. We say that we do, but even in those instances, we do it to say that we did it. Experience is still gain, even if only for satisfaction or bragging rights.
There is no way to escape the desire for personal gain in any action we take. Even good works done in the name of Jesus are for temporary personal gain. We are working for the magnified glory of OUR Savior, the increase of the Kingdom that WE are now a part of, and for OUR eternal rewards. Even the earthly blessings that come from obedience are personal gain. It may be for the glory of God, but we gain by association, and we want that.
God knows this. That's why Christians in heaven receive golden crowns. We earn them in this life. The only way to keep this accumulation away from prideful sin is to remember why we are earning them in the first place. We Christian's do good works for a single moment in heaven. Everything we do, we do for a single purpose. That event, that purpose, must be at the forefront of our minds, or we will fall into prideful sin.
John the Apostle writes about that moment in heaven. He writes, "(Christians) fall down before him who is seated on the throne and worship him who lives forever and ever. They cast their crowns before the throne..." - Revelation 4:10, ESV. Christians will bend their knees before God, throw their rewards at His feet, and say, "You deserve these rewards more than we do."
Remembering that moment will serve as the proper motivation and a filter in front of our brains, effectively guiding our actions while on earth and keeping us from the sin of selfish pride. We would be wise to go about our day saying, "I am doing this to win, but I will lay the reward for this victory before the Lord." - Pastor Mike.
BTW, I bet ninjas train in sneakers.