Ah, but what is discipline? Shifting the vocabulary burden around doesn't accomplish much. Discipline easily translates to will power (to do even in the face of adverse circumstances).

But haven't we learned recently to consider will power a finite resource? Something that cannot be switched on at will arbitrarily[0]?

The author himself escapes this accusation only by the skin of his teeth in the next-to-last paragraph:

   How do you cultivate discipline? 
   By building habits – [...]

Habit. This word, comparatively unprepossessing as it may sound, sits really at the core of the discourse[1].

Whenever my thoughts stray to punishing myself for lack of discipline, I try to remember to leave that martial outlook towards life to the Spartans[2] and reflect peacefully on my habits instead.

[0] Except, tongue-in-cheek, if you add sugar.

[1] Lest I leave an opening: It already is in Covey's seminal 1989 'Seven Habits', https://en.wikipedia.org/wiki/The_Seven_Habits_of_Highly_Eff...

[2] In this way, trying to force discipline may easily lead to results that are as devastating as those that the author foresees for motivational strategies.