One of my friends always says life isn't hard, we just don't always want to do what we know we should do (or something like that!).
...we always know which is the best road to follow, but we follow only the road that we have become accustomed to.
In choosing (or discerning Gods will) I think these two things are alike. Choosing to fight the good fight isn't hard, but sometimes we don't want to do it. But we do always know what is the best road to follow. Choosing to do so, this is the good fight. Not allowing ourselves to get caught on the comfortable path, but choosing the right path. This is fighting the good fight.