Phil. 4:13 -- we're in chapter 4 of Philippians this week -- is a gravely abused text. It's become a sort of slogan for self-achievement. But look at its context. Paul's saying, "I can do rich and poor, I can do hungry and filled, not because of anything in me. I can get through it simply because I have the strength that Christ gives me."
Paul's point is not that we can achieve anything we work for, but that God enables self-centered people to find their strength in Christ rather than in ourselves. The road to "all-circumstances contentment" is found in Jesus alone.
That said, let's don't be too quick to judge people we might think are misusing this text. At the Chicago Marathon expo a few years ago, an organization called "Team 4:13" had a booth where they shared the Lord with runners. I loved that. When offered one of their wrist bands to wear during the race I took it and gladly wore it. But my was I was tempted to be judgy!