Discipline roots from the Latin words 'discipulus' meaning ‘student’ and 'discere' meaning ‘to learn’. Even though ‘being disciplined’ suggests a rather inert virtue full of abstinence, the roots of the word describe a very active process of learning.
Making a change requires action, yet most of our actions are biased towards the default setting. Use positive default rules (i.e. automatic enrollment in health, educational, or savings programs) to take advantage of this inertia.
“Only the disciplined ones are free in life. If you are undisciplined, you are a slave to your emotions and your passions. [...] The best time to plant a tree was 25 years ago. The second-best time is today. Plant the tree of self-discipline.”
Eliud Kipchoge - Kenyan long-distance runner at Oxford Union (14:46 in the video)