Discipline is:

The consistent taking of actions that you believe will take you where you say you want to go.

"Consistent" because volume is necessary to get results.

"Actions" because actions are how you talk to reality.

"You believe" because you won't always know what you need to do, but you have to act on your best guess.

"Say you want to go" because you need to be clear in yourself about what you really want.

Questions to ask

If an action is not taking you where you say you want to go, why are you taking it?

If an action is taking you where you say you want to go, why would you define it as unpleasant?

If taking actions that you believe will take you where you want to go is unbearable for you, perhaps it is time to revaluate your strategy or what you really want.