woodfordr saidI agree man. Not all friendships are the same and without knowing details, it's just one big supposition. Some guys might think their friendship is going well while their friend is secretly scarred. In other cases the guy might be oblivious that his friend is outright in love with them, hoping they can friend their way into a relationship. How many of these guys are in relationships now? Cause often times the boyfriend might not want them to remain good friends with someone they slept with (adding another dynamic). We just don't know with such a thinly detailed study.
Even if you both are on the same page before the thing happens, one of you or both may come out of it changed, in terms of how they look at the other person. It doesn't even have to be related to deeper feelings one develops for the other than will most likely remain unrequited. But some people feel so bad and disgusted sometimes by the act, that the friendship has no chance of survival. And this is quite common too, and I've seen it happen with some of my straight friends.
And it has happened to me too, when I was younger and was fresh on the dating scene. I landed with my feet deeper in the water than the other person was willing to follow suit, and so I got burned. It was pretty much the moment I put an end to hook ups and weekend adventures.