It's the Anna Karenina principle: all good forward rolls are the same, but each bad forward roll is bad in its own way
For those who don't get the literary allusion, please, take the time to look it up before you jump all over this. The point is that there are many things that can be wrong with a roll (and in giving advice, people tend to focus on what was wrong with
their rolls as being The Key for everyone else's forward rolls), and they all have to come right for the roll to be good.