when you have a broken bone.
they tell you to use it a little to strengthen it but don't put too much pressure on it too soon, don't pusher harder than it can go in its broken state. if you work it too hard before its had chance to patch itself up properly then you'll just make it worse and it'll take longer to heal. you have to accept that its not as strong as normal and it needs rest and a chance to be looked after so it can get better and you can get back in your dancing shoes. they tell you to be careful but don't be afraid to use it, in small bursts, be gentle and don't expect miracles in a day.
i know exactly what they're talking about.