To have to or not to have to

It comes up a few times a year; a lesson with have to and must. And every time, I have to (or I must) get out the grammar book to relearn the differences. I apologize for not knowing and explain that in the US we use have to for almost everything and that's why I'm in doubt. Grammatically speaking, the difference lies in the obligator. If I obligate myself, it's one of the two and if someone else obligates me, it's the other. But don't forget, I don't remember.  

I really should know the difference because it's become my mantra. I have to write. I have to study. I have to start the Christmas cards. More than one therapized-friend has encouraged me to stop saying it. They tell me I should be saying I want to. They say I'll never do things if I think I have to do them, but if I want to, I will. According to them I have to/must pay more attention to my vocabulary. To which I reply my lack of doing has nothing to do with my word choice.

Last week my French teacher and I were trying (because I can't really speak French) to talk about traveling. She said she seldom makes plans in advance. She hates feeling like she has to go to Rome just because she's already bought the train tickets and reserved the room. She likes to feel free. Unsure if she should have said she has to or she must go to Rome, I made no correction there. Instead, I questioned her need to feel free.

As a fellow freedom seeker and part-time therapist, I was proud of my observation. I've always defined my aversion to advanced bookings as giving up control. But her romantic (and perhaps therapeutic) choice of words was that she liked to feel free. If it's as easy as that to go from being a control freak to a free spirit, I want to start choosing my words more wisely.