Paradoxes like this always frustrated me so I worked-out a more concrete model for these change systems:
You've got "area of behavior" which you've got good conscious control over and where you can plan and work hard. You've got another "another area of behavior" where you don't have much conscious control and you tend to screw-up in.
You want to work hard within the area you do control to create a framework where things are relatively easy for you in the area you don't control.
You don't want to just throw a lot of effort at the area you don't control, you don't want to discourage yourself concerning the area you don't control. You want to have clearly understandable goals in the area you don't control.
And so you want the "heavy lifting" to be within the area you do control.
Now, "hard" is for the work in creating your framework. "not difficult" is for the experience you have within the framework.
Definitely. I think that it applies to their method too - setting up the triggers and making the behaviour easier is the "hard" part within your control.
tldr: start small, don't set bullshit goals, it acually is hard. much harder than you think