to achieve the aim

I have recently started treatment (medication and therapy) for what my doctor/psych describe as 'major depression', present since I was around 10 (now early 20s). Both of them think that a contributing factor is the pressure I put on myself to do well, and say that I should 'relax' and 'accept that I'm doing the best I can'. I'm not really a perfectionist (as I've never really done anything perfectly anyway) but I can't really imagine what else people aim for. How do you know you're 'doing your best'? Can't you always try harder? Complication: I am one of those ridiculously lucky people who seem to be able to do anything. Academics, sports, music - I can pick up any area and do better than average without trying. Perhaps related: I don't try. It's so much effort, and why bother turning up to class/training to get fitter/whatever when I'm already better than most people and I probably can't be as good as the best? On the other hand, how can I possibly be happy with second class honours when I only attended two classes for the semester and did the assignments the night before, and it's only second class, and I might never get a good job because I don't have either excellent marks or good work habits?