How do you maintain your discipline

[Obs]

Disclaimer: There isn't a section on the forum that this question can fall into nicely so I have decided to post it in the lounge, however it's not for bullshitting or joking around in... I'm only interested in genuine, helpful responses.

So as the question says.... How do you maintain your discipline? I'm perhaps not asking about motivation.... as it is easy to do something you want to do. I'm talking about when you really don't want to get out of bed on a morning when it's freezing cold to hit the gym, or when your life is so busy that you want to go home and eat shit but go to the gym instead....It doesn't have to just be discipline towards the gym or eating right..... just how do you make sure shit gets done?

I usually maintain my discipline by answering pm's with a yes or a no regarding shit that actually matters.