Salt

If you want to fully enjoy some Italian spaghetti, you must salt the water you boil them in. Tomato sauce and parmesan cheese are important but, if you forget the ingredient "salt", the taste of your dish will not be enhanced to its best. The same happens to your life if you don't add enthusiasm to your endeavors.  Good will, dedication, perseverance, commitment are all indispensable features of a successful action. But, if you lack enthusiasm, your work won't be totally fulfilling, as a saltless dish may be healthy but also tasteless. You might prefer to replace salt with a herb or a spice: what counts is that little "extra stuff", that simple seasoning that allows you to fully enjoy what you are eating - or, out of metaphor - what you are doing.