Both here and in the next verses the Preacher gives yet another example of someone who wants to be rich but who as a result lives an unhappy life. This man does not enjoy his wealth. He does not even want to enjoy it. He just wants to have his capital grow. He makes his own life miserable because everything revolves around his possessing more and more. As long as his bank account is growing!
He doesn't have any use for joy in life, no matter how rich he is. It is an annoyance for him to have to spend money. This is what Ecclesiastes 5:17 points out: All his days he eats in darkness; his whole existence is full of misery and sorrow and full of discontent.
13 There is a grievous evil that I have seen under the sun: riches were kept by their owner to his hurt,