What a wonderful topic!
When I got married in 1971 I was very young but I had no idea of an "out" if things got rough. I just didn't think that way.
Maybe it was seeing my parents, aunts and uncles, etc in long marriages. Times were different too.
Out of 4 of us kids 2 are divorced and 2 are still married. Those 2 divorces were sad but both my siblings are happier now. Neither has remarried. The one still married is miserable. I have seen both sides of long marriages so I don't like to judge what people do.
I go by the 3 A's- adultery, abuse, addiction. If any of these are in a marriage something has to be done. I have dealt with addiction in my marriage and it's put a huge strain on it but we're working hard on it as I speak :)