I struggled to get myself to the gym. It’s a classic trap, and I suspect many of us can relate to it. My sister was one of them, too. But she used to tell me: The best workout is the one you actually do. Her words have stuck with me ever since she first told me. They’ve helped me adjust the bar when I’ve felt resistance to going. Instead of telling myself I need to have a proper workout, I can think: I’ll just hop on the bike for a few minutes. Then I can reward myself with a nice...