When you're in the middle of something you enjoy, time just flies. Whenever I'm out for just a nice run, without worrying about how fast I'm going, I just realize that I'm flying along and going at a decent pace. When you're just on cruise control, you're just going at the pace you're body is telling you to go at. You're not running too fast where you're tiring and you don't know how much strength you have. You're not so slow that you're not going anywhere and you feel like you're not doing anything. It's the point in between, where you're comfortable and enjoying the ride.
Sometimes, people get focused on improvement that they forget to enjoy life while they're in the midst of it. Other times, people get focused on the fun in life, forgetting that they need to work on themselves and see how they could get better. Balance is once again, the overall theme, where the individual needs to understand what that point is where you get both enjoyment and improvement. No matter what we do, we can't go one extreme or the other, because in doing so, we lose value of the other. It's important to work on both at the same time, because it gives the best improvements.
Working too hard to produce results will backfire and end up hurting the individual, while enjoying life too much will end up causing the individual to lose that focus on the task at hand. Both are important, but at the same time, it is necessary to have both at the same time.
Cruise control helps you go at a constant pace. In a car, if you go on the interstate, you can go on cruise control, which will automatically help you save gas when you're going on a flat surface. Should you choose not to do that, the slight variation in speed will not maximize the efficiency of the vehicle. In the same way, it's important to let your body know what it can handle and get on that cruise control.
(forgot to mention that I cycled 5.05 miles in 18:33 and ran 8.8 miles in 1:17:36, an average of 8:48 min/mile. During that run, I was on cruise control and just taking it easy)