MRH, you have to when circumstances leave you no choice. It matters not whether those circumstances arise from without or within.
I don't want to go off on too much of a tangent, Sentipente, but that statement and position is a very difficult one to defend. Because there are really only two things in life that you
have to do, namely (1) pay taxes, and (2) die. With those two exceptions, you
always have a choice.
Of course, if you don't do something, there are always
consequences. But you always have a choice, and you don't really have to do anything, as long as you're prepared to accept the consequences for not doing it (whatever the "it" is)!
That said, just to humour you, I will accept your definition of "have to" for now!
Your statement,
Humans don't change unless they have to.
just doesn't hold water!

Byfaithalone has already agreed with me that he changed his dietary habits when he didn't "have to"!
I would say (and you can debate me on this if you like) that people change under one of the following three conditions and only under one of the following three conditions, namely (1) when they have benefits to gain by changing, especially when the benefits outweigh the price they pay for changing, or (2) they know that there are going to be consequences if they don't change, or (3) both.
I know that you mean well, sentipente! But your saying, "Humans don't change unless they have to," just doesn't make sense! If you think it over, I am sure you will agree with me!
God bless you, sentipente!
With love in Christ,
Mark