The commencement address by Steve Jobs at Stanford University in 2004 offered one of the finest insights in the recent legacy conversation about personal priorities. Jobs used a comment made by Aristotle a century earlier to illustrate his main point about the limitations of “willpower.” Aristotle asked rhetorically, “How could such a wit as Aristotle have existed?” Jobs replied, “I don’t know, but I think the answer is self-discipline.”

He means that the primacy of will power is not a fixed, intrinsic quality of human nature and that, indeed, with discipline it can be harnessed to powerful effect. That’s why it’s important to choose your priorities carefully, that is, to live your life as if you were determined to bring about a greater good.

Steve was partially right about the limitation of will power, but did not address the important alternative. It is what constitutes the second primary source of energy–that is, the quality of what we strive for in our lives and work.

Here’s how to remember Steve’s point: I’ve spent much of my professional life searching for this second source of energy. After carefully studying many of my peers, I’ve found that our psychological well-being is intimately linked to our mental focus, especially our capacity to engage in sustained effort, whether it be our motivation to find a solid job or to invest heavily in our career. In short, being committed to something that’s important to us is an effective generator of self-discipline.

Perhaps the most powerful anecdote about discipline comes from motivational guru Tony Robbins’s latest book, Like Water on Stone: How You Can Master Your Mind, Set Your Goals, and Reach Your Highest Potential. It details how Robbins drew inspiration from Aristotle’s remark that “deluding ourselves into believing that wisdom and genius must wait until an event occurs is not wisdom but delusion.” Robbins points out that people who made the most valuable and worthwhile decisions over the course of their lives, the ones with the most enduring success, transformed their “willpower into decision.”

It’s not for nothing that Aristotle labeled the Third Metric (pronounced, loosely, as “whole”) as one of the core teachings of psychology and public philosophy in the first millennium CE. By demonstrating that success derives from building people’s “whole person,” instead of just their skills and talents, it helps explain how our lives have meaning and purpose. Aristotle’s other works, including the works of his son, the great practical philosopher Heraclitus, were committed to what he called the Theory of History:

Great men, Aristotle said, emerge from the dustiness of ordinary, mortal lives, insisting on a “philosophy of nature”…Because of the principle of “right works for wrong works,” which demand a little more of what we have than a sheer want of it, the virtue of diligence and wisdom, which must be experienced in order to acquire them…or, that is, to possess right means of becoming a man of good works.

You have to experience what you desire first before you know how to acquire it, a principle of Western philosophy that’s been percolating through the practices of many different masters over the past several centuries. Once you know how to achieve what you want, you can then turn your attention to using willpower to achieve whatever else you desire.