The grass is always greener on the other side.
Regardless of how good our current situation is, we can always find, or at least imagine, one better. This is true across our whole spectrum of experiences: jobs, vacations, homes, cars, opportunities, and even relationships. In our minds at least, we entertain that there is something superior we are likely missing.
This sense can cause us to cause us to abandon our present situation, often in mind but sometimes in body as well, in pursuit of an apparition.
Paul is specifically speaking on marriage in this passage, but the truth he relays transcends topic and provides ubiquitous application regarding contentment: to experience fulfillment we must be present.
It is easy for our minds to wander and imagine what could or might be, and in doing so abandon what presently is. This lack of presence unfortunately deteriorates our current situation and in doing so increases the contrast with our sought scenario in a spiraling self-fulfilling prophecy. The truth is there are people who need us right where we are, right now, to make whatever situation we find ourselves in work.
Paul says, “God, not your marital status, defines your life.” But I think we can extrapolate this passage out and substitute almost anything: God, not your job title, not your house, not your net worth, not anything else, defines your life. And we need to stop allowing it to do so.
Ultimately, contentment is not something we find but something we choose. We can spend our whole life on an empty search or we can choose to be content here and now. What will you choose?