I try to view problems as opportunities. If it's raining outside, that's training in the rain. Snowing? Awesome, snow running! Too hot? High-temperature training. Too cold? Low-temperature training. I'm too tired? Fatigue training. I also try to look at things from what I call a "mediative" point of view. So let's say I'm out running my regular route but it's cold, windy, raining, etc, and I feel miserable. I try to remember how I felt running the same route on a beautiful day and bring my mind back to that state. Or if I'm fatigued, I try to remember a day when what I was doing felt easy and set myself the challenge of trying to regain that mindset. Again, it's about turning problems into opportunities: fatigue is an opportunity for fatigue-mastery. It helps to take an interest in the mental element of training, sports, etc, so you can think of mastering mental adversity as part of your training.