Eric Cressey wrote a great post about putting your client's goals ahead of your methods - you can read it here. Emotional Detachment for Training Success
He makes a great point - you want to be emotionally attached to your client's goals, not the route to the client's goals. Not your goals, either - if your goal is maximum fat loss but your client only cares about weight on the bar, your goal doesn't matter. You need to train around what the client needs.
In fact, you can (and probably should) build your operation around your client's goals, not your methods. If you had to either fire a client or let them do something you don't normally do (say, avoid squatting, or do slow cardio, or do sit-ups) that fits their likes and goals, which would you choose? As a trainer, I feel the answer must be "let them do it." It's about them. If it's something that, as a trainer, you just can't do well, then speak to them and see if they want to adapt to what you can provide or change trainers.
For a trainee, this is equally important advice:
Marry yourself to your goals, not your methods.
If you like, say, lifting heavy weights or running sprints or doing slow cardio, that is great. Do it when it makes sense for your goals and enjoy it. But don't do it when it doesn't meet your goals.
If your goal is to just enjoy the workout, then choosing what you like to do is fine. It's the journey not the destination, so choose the journey you like. But if it's about the destination, pick the route that gets you there, not the way you most like to travel.