I have learned to be content whatever the circumstances.
The Puritans used to call contentment a rare jewel. Rare indeed! How many of us can truly say that we have learned contentment whatever the circumstances? We can be content under certain circumstances, but "whatever the circumstances". Well that's a little more demanding.
There's a clue to Paul's solution when he says, "I can do all this through Christ who gives me strength." Paul has made a decision that he will view his life only from the context of serving God. He looks to Jesus Christ for his contentment. In Acts 20 he declares that his life is worth nothing unless he completes the work God has called him to do. In Philippians he speaks about counting all as a loss, of death as gain and service as continued joy. His perspective is crucial to his contentment.
So how content are we? Do we drift through life and think we're content, or do we strive for more things in order to feel better about ourselves? Neither is right. Paul held nothing back, he went after the things of God with passion. He never drifted. Don't mistake apathy or inaction for contentment.
An American president was once asked, "How much money is enough?" He replied, "Just a little bit more." If your contentment comes through gaining that little bit more, you will be disappointed. But if you invest your life fully in the purposes and mission of God, then contentment will surely come as you find your fulfilment in serving God wholeheartedly.