When you think of it, there is a reason why exercising is called working out. There are so many parallels.
First and foremost, different people have different reasons for working out, some do it for the sake of doing it, some enjoy doing it, some do it for the end results and some are advised/initiated by their family/friends/doctors into taking it up.
Some people love working out in a gym while others like to do it within the confines of their home. Each person has its own set of favorite equipment and exercises. Some like to stretch out on a mat while the others sweat it out on the treadmill. There are those who find the gym ball fun while other might like to do the weights. Just like each work is important but different so also the different form of exercising. Who is to say that aerobics is better than yoga or weights training. It depends on your attitude, aptitude , metabolism, body type, unique circumstances and most certainly what you are trying to achieve. Depending on your attitude you might prefer to go solo on a treadmill or join a group for kick boxing.
Some enjoy the process all along while others can wait to finish it and get done. Some do it with music while others are totally focussed on the dials. Some micromanage each micro-gram and calorie while others lose focus of what it was that got them into this and do anything at random.
To some it is a form or relaxation and for others it means a lot of pushing and pumping to feel the rush of the adrenalin. Some love all the action and excitement that it adds to their life while others to calm their frayed nerves.
Some come to run away from others while others join a gym to meet more people. The way you chose where to work(out) depends on various factors, the equipments, cost, timing, culture, availability, distance or simple brand recognition - and there are those who just like to 'belong' to a cool club.
Some are self driven and push themselves to newer limits each time. Others need the goading from the trainers to continue. Just like at work, a good trainer/companion can have a lasting impact and make all the difference between loving it or hating - not to forget success or failure. Doing it wrong or not following the rules can be disastrous.
Different people achieve different amount of success. Then again, different have different goals and define success differently. Take the case of the simple treadmill. Each person chooses a different workout with the exact same equipment - just like at work. They choose a different program, a different timeout, a different gradient, a different speed. Some do it fast but don't last long. There are others who are slow but go far. Some others ramp up fast while others like to go gently. Some put a time limit (9-5??) while some put a limit in the form of calories (Finish this work and go). Some would work hard enough until they get their hearts pumping!
Just like at work, if you are doing all right, you go achieve a higher goal each time. The fitness level just like success at work is a factor of many things, your training, your trainer, your hard work, the right equipment/tools, your perseverance, your metabolism (smartness??) . Just like at work, experience and age play some role but only some.
I could go on and on .. I love analogies, patterns, abstract stuff but I guess its enough for now.