There are a lot of things that I'm not very disciplined about - shaving, finishing books I've started reading, and writing letters. But, there are three things that I try to do every day: walk the dog, read to my son, and lift weights. If I don't have an outstanding session, or miss a day because I'm sick or overwhelmed, I don't beat myself up about it, but understanding that motivation is overrated and maintaining the right habits is all-important, I try not to skip for silly reasons.
The mind is quick to give reasons why I should take a day off; why I need a day off; why I deserve a day off. On those days when the mind is protesting loudly, I tell it "Not today. If we really need the rest, we can be lazy tomorrow. Today is a good day. Keep moving."