As in everything, this is fully dependent upon the people involved. I hate the statistics that are tied to these things as if failure is inevitable. (Not saying all say that).
My wife and I are a perfect example of how things can work, even if they worked the “wrong way”. Just last week we celebrated our 25th wedding anniversary, and God willing, we will celebrate our 50th with even more joy.
We lived together two years before getting married. Yes, we were young, barley 18 and 20 at the time, and did it for a number of reasons, not the least of which revolved around wanting to make sure things were right, how it would be, etc. etc. Was it the right thing to do? I don’t really know. All I know is we turned out fine, happy, and are still in the process of raising our wonderful children.
With that said. Do I think it is the right thing to do now? No. I realize why it’s considered wrong by many, and don’t know if I would ever want my children to do it that way. In the end though, I cannot deny that it worked for us. Sure, it would have worked having not lived together first, however, we did, and things were and are fine in the end.