This is missing the most important step: get out there and practice.

You're not going to succeed at steps #6 and #7 in situations as dire as what the author describes without practicing a bunch. You have to choose low stakes, real situations to gain experience:

* a cashier asks you if you want to round up by donating to charity

* a friend asks if you want to do an activity with them, and you do not want to do that activity with them

* someone suggests splitting the check down the middle, but you only had a tiny side salad

* etc.

You can of course handle these however you want. But if you want to learn to set a line when it's important, you should have already practiced in a dozen or so cases like this, without apologizing: No, thank you / No, I'm not into that / I'm leaving enough to pay for my tiny side salad plus a nice tip

Practice doesn't guarantee you won't buckle in tough situations. But you'll definitely buckle if you don't.