The central message of this sermon is that the pursuit of self-improvement and personal success, as popularized in modern books on positive thinking and productivity, is ultimately futile. The teacher argues that this idea has been around for thousands of years, even being addressed by King Solomon in the book of Ecclesiastes, which presents a pessimistic view of life under the sun. Solomon undermines every option and hope that people think they have for controlling their lives, including wisdom, pleasure, and even God's favor. The teacher suggests that this is because human nature is prone to frustration and disillusionment with the unfulfilling nature of material success and intellectual pursuits. Instead, Solomon turns to a more affirmative message in chapter 11 of Ecclesiastes, encouraging people to cast their bread upon the waters and enjoy life despite its meaninglessness. The takeaway is that true happiness and fulfillment can only be found by accepting and embracing the limitations and uncertainties of life, rather than trying to control or improve it through human effort alone.