Adam Clarke on Proverbs 13:12

Hope deferred maketh the heart sick - When once a good is discovered, want of it felt, strong desire for the possession excited, and the promise of attainment made on grounds unsuspected, so that the reality of the thing and the certainity of the promise are manifest, hope posts forward to realize the blessing. Delay in the gratification pains the mind; the increase of the delay prostrates and sickens the heart; and if delay sickens the heart, ultimate disappointment kills it. But when the thing desired, hoped for, and expected comes, it is a tree of life, עץ חיים ets chaiyim, "the tree of lives;" it comforts and invigorates both body and soul. To the tree of lives, in the midst of the gardens of paradise, how frequent are the allusions in the writings of Solomon, and in other parts of the Holy Scriptures! What deep, and perhaps yet unknown, mysteries were in this tree!