I was about to leave work when I saw a co-worker walking around trying to find someone to give their car a jump. I'm no car mechanic, but I did have some cables, and had used them before. So we go outside and I drive my car over. I looked at the instructions for a minute, then proceed to successfully jump their car out in the pouring rain.
It felt good. Very good. I'm glad I could help them out. It was kinda fun actually. I was thankful that I had the chance to do this before and that I had been taught at least a little bit about cars.
But after a while I realized something. There was a bit of a temptation to congratulate myself too much. "Great job, you did it!" "You are awesome!" I recognized this for what it was. Sin.
Of course you will feel good, and maybe you really did do a good job of going above and beyond. There's no harm in feeling good about doing that. But - the second you switch your focus from being thankful you could help others to praising yourself, inflating yourself with pride, even thankful that you alone were able to do it - that's where you start to fall down spiritually.
Always keeping your focus on God and others keeps this problem at bay nicely - although that's easier said than done.