Treadmills are wonderful - you get on, you exercise, and then you get off. That last part is important. You have to get off when you've done your workout. Staying put is not a great idea. The same thing is true for those mental treadmills we find ourselves on. Sure, stay on - for a while. Use the time to work out whatever it is you have to work out as much as you can manage for that day. Then get off. What cripples us is staying on the same thought, day after day, working hard and never getting any further with it because we've become habituated to the mill, rather than using it for what we need it for. Watch out for those mental treadmills.