Okay, so what if your friend's boyfriend had sat her down and said this:
"Look, I know you want to enter this program. This is a huge deal for you, and you've talked a lot about it. But after thinking it over, I have a few reservations. The first is that you're going to only be able to work part-time during the program, and you'll be paying tuition. Overall I think you're going to end up losing about eighty thousand dollars in lost wages if you do this.
"And I'm thinking, you don't have eighty thousand to lose. Each of us doesn't have fourty thousand to lose. I think our relationship is going to go the distance, and if it does, I'm scared by the thought of beginning our marriage with a huge debt. Debt at the beginning of the marriage is going to impact our ability to buy a house and it's going to profoundly color our decision-making process as to when or if to have children and how many to have. I'm not sure the program is going to enhance your marketability enough to make up for it.
"But you've been thinking about this longer than I have, so I was wondering how you've reconciled these issues and what we might be able to do to reduce the impact of your lost income. The other thing, and it's kind of scary to me, is how much of your time will be invested in this program, and whether we'll be able to spend time together any longer. I know that's maybe silly of me, but I'm going to miss you if you're busy six nights a week."
THat would open the door to discussing compromises, ways of meeting his needs and her needs at the same time, etc. What you've made it sound like is that the boyfriend said, "Are you nuts? You're going to put us eighty grand in the hole! Who needs that? This program is useless. Don't do it." Which, IMHO, seems like a move to keep her dependent on him and prevent her from being a fully realized person. (RUN! Run like the wind!) Instead of saying, "I'm going to miss that program," she should be saying, "I'm going to miss him."
Now your situation sounds more like the above good conversation. "Sweetie, I remember when you wanted to become a firefighter, and I thought that was good and I supported your decision. But after being afraid several nights while you were driving the armored vehicle, I'm realizing how tough it is for me to think of you in a dangerous line of work. I'm scared for you. I don't know how I'd cope if something terrible happened to you. So I wanted to know if you still wanted to go for the firefighting thing, or if you were planning to work as an EMT for a few years. And if you had thought about the danger aspect of firefighting, and if you know of ways that other firefighters' wives cope. Because it's going to be hard for me to support you if I'm so scared for you."
Phrasing it in terms of your needs and his needs, and meeting both of them simultaneously.
It becomes an unreasonable expectation when one person feels entitled to the other's capitulation OR when one person is the only one making compromises. Or when one person is changing the ground rules of the game mid-stream. ie, I married you knowing that you love your extended family and want to visit them every weekend, but now I want to move you 2500 miles away from them.