Have you ever tried to get in shape by going to the gym?
You make the decision that you want to improve your health and fitness, and buy a gym membership to do it.
But then what? You enter the gym, and you suddenly take in all of the options available to you. You need to pick what type of exercise to do, what equipment to use to do it, and how long to do it for. There are so many potential choices to make, that it becomes nearly impossible to make a choice at all. There is an easier, simpler, and more effective way, however.
In gyms, people who want to get in shape hire personal trainers so that the trainers can help guide them through the personal fitness process.
The customers tell the personal trainers what goals they would like to achieve, then the trainers come up with a schedule, diet and exercise regimen that would help the customer achieve those goals most effectively.