i think that if you do something physical everyday, then you don't have to be so hard on yourself when you do go to the gym and don't do a super long, hardcore workout. in talking with different personal trainers, a couple of interesting things have come up.
1. cumulative exercise-this is helpful, especially if you are busy-it means that all the exercise you do in a week ADDS UP! But it doesn't just apply to going to the gym. this can be taking a walk on your lunch break, walking up the stairs instead of taking an elevator, biking to work...etc...
2. our bodies need different types of movement! not only does doing the same routine at the gym get boring, but it turns out to not be the best idea. the trainer who told me this is a sky coach and he said a lot of top athletes incur injures because they focus on only one thing. so, mix it up! even if it's not at the gym, it does count!
the main thing is to move your body.
...that was longer then i thought it would be, sorry!