There’s not usually time to get bored during track workouts because you’re doing shorter segments, but they hurt because you’re working hard. So for each segment, focus on one particular body part or technique. For instance, on one 400m repeat, think about nothing but making sure your hands are where they should be. On the next one, focus on your knee lift or getting your heels up toward your butt. When your attention is on one particular aspect, you’re less likely to be thinking, ‘Oh crap, this hurts!’.