There are times when I am on the elliptical and all I think about is that I want to stop or become complacent with my work-out. When you start to meet exercise resistance a good strategy is to stay in the moment. A tried and true method of staying present is to target your breathing. For Example, notice how long your inhales and exhales are. You may notice that the air going into your nostrils feels cool, while the air on your exhales feels warmer.
In focusing on your breathing instead of your thoughts you can remain more involved in your training. Another focal point can be your form. Pay close attention to how each of your limbs feel. Mentally scan your body for points of tension. Imagine breathing into those points of tension to give yourself a more relaxed stride. By clearing your mind and centering on your form and posture in the present moment you become less pre-occupied with negative thoughts. Never, ever resist a wonderful work-out!