It is so easy to get upset when we're working our tail off and those who are slacking seem to get the same (or better) rewards.
You know what? Our attitude toward our work is what really matters. Does someone else's lack of work really affect how you should be doing your work? Nope. Sure, sometimes their laziness could make our job more difficult, but does that mean we should compromise our work just because they do? Again, nope.
It's also so easy to get upset when we begin to think that nothing we do is as good as what someone else is doing.
You know what else? God did not create us all with the same abilities. And that's perfectly ok. In fact, it's just plain perfect! If all of us were the same, this world would be a pretty boring, unproductive place.
You are serving God's purpose in your work (and by how you complete your work). Don't forget it!