The heart of man is a slippery thing: when matters go well, it falls into presumption; but when matters go badly, it falls into despair. This is why ours must be a mixed lot. God must throw one care after another into our prosperity, must salt it for us, and must dampen our high spirits with apprehension so that we stay with the First Commandment...Our troubles must also be tempered with some consolation so that we cling to God's promises and do not tempt God, who would be our God. In this way a man stays on the right road so that he does not despair in trouble but always stays standing and praises God, whether he fares well or ill, whether he wins or loses.
(What Luther Says - #682)