Be an animal

In nature we would have been much stronger from running around, hunting and climbing. Human muscles are perhaps now relatively some of the weakest in the animal kingdom, This should be more than enough reason to go to the gym!
The reason for the above is that an animal's life style is far more active – we train for an hour and sit down for the rest of the day whereas animals hunt and run all day. Try to do something physical as often as you can – not just in the gym.