John Wesley on Ecclesiastes 1:18

Grief - Or, displeasure within himself, and against his present condition. Sorrow - Which he does many ways, because he gets his knowledge with hard and wearisome labour, both of mind and body, with the consumption of his spirits, and shortening of his life; because he is often deceived with knowledge falsely so called, and often mistakes error for truth, and is perplexed with manifold doubts, from which ignorant men are wholly free; because he hath the clearer prospect into, and quicker sense of his own ignorance, and infirmities, and disorders, and withal how vain and ineffectual all his knowledge is for the prevention or removal of them; and because his knowledge is very imperfect and unsatisfying, yet increasing his thirst after more knowledge; lastly, because his knowledge quickly fades and dies with him, and then leaves him in no better, and possibly in a much worse condition than the meanest and most unlearned man in the world.