The Futility of life as it is characteristically lived out ‘under heaven’ is captured here in terms of people trying to straighten what is twisted and to count that which is ‘lacking.’ The key to understanding the first line is found in 7:13 ‘Consider what God has done: Who can straighten what he has made crooked?’ The emphasis there and in 7:14 is on accepting what comes from the hand of God rather than striving with and struggling against it.
Provan, I. (2001) Ecclesiastes/Song of Songs: The NIV Application Commentary, 77
One of the most comforting passages in the New Testament is Paul’s statement that “for those who love God all things work together for good, for those who are called according to his purpose” (Rom. 8:28). We must be careful here. Paul does not say that everything that happens, considered in and of itself, is good. Nor is our theme song “Que Sera, Sera,” “Whatever will be, will be.” We do have the astonishing promise, however, that everything will work together for good for those who love God and are called according to His purpose. This means that even from the bad things that happen to us, God is bringing about good. This glorious concept means that we should trust God—even in the midst of tragedy, pain, disease, and suffering of all kinds. God assures us that He is working all things together for our good.
RC Sproul, Is God in Control of Everything?
The human attempt to impose self on reality in this way is a foolish undertaking, which can only end in pain and frustration. Human goals should be set in accordance with the nature of reality, not in defiance of it; otherwise human existence becomes embroiled in pointless striving.
Provan, I. (2001) Ecclesiastes/Song of Songs: The NIV Application Commentary, 58-59