"I don't have time"
Sure, you're busy. And of course you have to decide what to prioritize each day, but when you say, "I don't have time to exercise," what you mean is, "Exercise isn't a priority." Let's just call a spade a spade.
Dr. Pamela Abramson-Levine, a family practice chiropractor in Santa Monica, California, doesn't hesitate to call her patients on this one, "When that excuse is given to me, I look at their intake form where they wrote that they watch two hours of TV per day. Then I show them how they can fit in some exercise while watching TV. Or sometimes I'll ask the patients if they have five minutes. They almost always say, 'Yes, but that's not enough time.' Then I show them exercises that take five minutes or less to perform."
As Abramson-Levine points out, "Something is better than nothing," and if you have five minutes here and there, that's better than skipping exercise altogether. It's about priorities, not time.