My daughter just told me last week that she finally understood "sufficient to the day is the evil thereof" and asked for more scripture surrounding it, so that she can do better with her problem of projecting into the past and future.
It was taught to me that looking into the past causes depression and looking to the future causes anxiety, two major problems I've had in the past that amped my stress.
To handle stress on a moment-by-moment basis, I always remember something a good friend told me. He said "is it better to be right or happy?" Then I started practicing on a momentary basis. In the beginning it took a lot of banging my head on doorjambs to finally give my problems to God. It took proof that I performed better, was happier, and could actually change stressful situations if I wasn't stressed that sold me on the deal.
Oddly enough, cigars were a big part of that learning process. When I could finally sit long enough to smoke a cigar instead of trying to master my life, I knew I'd come a long way.