Dictionary definitions: enthusiasm, energy, excitement, piquancy. Zest correlates highly with happiness. Realistically, you may have to spend a fair amount of time in dutiful activities. Commit as much time to the activities which make your energy surge. In fact, try to inject zest into some of the more ‘boring’ activities as well. Break old habits, make it a competition, try to win. Hang out with real enthusiasts, even if you don’t share their passion for tiddlywinks or train spotting, and discover the secret of enthusiastic pursuit of your interests. Then apply it to your life.