The Wheel of Life is a picture of how satisfied you are with each part of your life, drawn so the uneven parts are obvious. Eight slices, a score from 1 to 10 on each, shaded from the centre out. A wheel with every slice at 7 is round. A wheel with a 9 for career and a 3 for health is lopsided, and the lopsided part is the point: you can see in one look what a list of eight numbers makes you work out.
The exercise is usually credited to Paul J. Meyer, the founder of the Success Motivation Institute, and dated to the 1960s. The coaching references that say so do not cite a source, so we repeat it as the usual account and no more. What is not in doubt is how widely coaches use it, and the reason is simple: it turns a vague "things are not right" into a named area.
Three things make the exercise more useful than it looks. First, score how things are now, not how they were last year or how you hope they will be. Second, read the shape before the numbers: the slice that surprises you is often more useful than the lowest one. Third, change one thing. The wheel names your lowest area and gives one small habit for it, taken from an article on this site with its study linked, because a single habit you keep is worth more than eight you plan.
Most of those habits are about how to start rather than what to achieve. Implementation intentions turn "sort out my money" into a plan with a time and a place, and tiny habits shrink the first step until it is hard to skip. If you want to see how long a new habit usually takes to feel automatic, the habit formation calculator draws the published ranges. The wider case for small, steady change is in the self-improvement guide, and the numbers behind it are in small habits that change your life.