Some examples: If you want to excel at your job but you're eating poorly and not exercising, your physical energy and mental clarity will be compromised, causing your job performance to suffer. If you spend too many hours at work and never take any time off to unwind, ultimately you'll burn out and get sick. If you want to start your own business but are unwilling to stretch and take risks, it's not very likely you'll ever be a successful entrepreneur.

To begin the process of building your endurance for improved personal performance, it's best to identify the area of your life in which you are weakest. For one person, that may be the poor relationships he has with co-workers. For another, it may be afternoon tiredness fueled by too many sweet carbohydrates during the day. "Train" yourself in this area until you gain those skills, much like you would train a specific muscle you want to develop in your workouts. Set small goals for change and follow through with them.

For instance, someone who is a workaholic could commit to taking small blocks of time off to relax, eventually leading to a whole week, even two weeks off (gasp!). A shy office worker might make a point of saying hi two or three times a week to associates never spoken to before, leading to an invitation to lunch. The person with poor collegial relationships might commit to having a brief personal conversation twice a week, leading to office meetings to discuss better ways to work together.

An exceedingly important thing to remember is that whenever you expend energy, make sure to give yourself time for renewal. Just as muscles are strengthened by subjecting them to stress and then giving them recovery time, it is also possible to strategically build the "muscle" of self-control or empathy or assertiveness or passionate living. The same concept can be applied not just to self-control, but to anything, such as being more organized, more accepting, more focused, a better parent, etc.

"Exercise [these qualities] past normal limits and then allow time for rest, and these muscles become progressively stronger," write Loehr and Schwartz.

Whether it's an area of your work or your personal life you want to improve, it's not about how much you do but how well you manage your energy.

Teri, the overworked mother, finally spoke to her boss about cutting down her overtime hours. She also arranged for her husband to watch the kids two nights a week so that she could attend a dance class and for a few hours on the weekend so that she could work for a favorite political cause. As she began to reap the emotional, physical and spiritual benefits of these activities, she found that her work performance improved—even with less hours devoted to it. And her general outlook on life once again became positive and inspired.