I believe it is a myth.
NO ONE is perfect, though there are people that we will match with better on many levels. But those are fewer than we like to think, I do not believe in Mr Perfect or Mr Right. True that there are some very rare couples that seem to be perfect in every way, but majority if not ALL instances of this type of relationship like any other relationship takes a LOT of hard work to function.
So if one thinks that there is some one out there who they could be with that would make for an effortless and always %100 happy go lucky heated romance and all of that, I would be very comfortable stating that they are wrong because 99.99% of my estimation would be correct if not %100. Humans are and never will be perfect and some one is always going to go against the grain with us at one time or another regardless, and well it is up to us to use our evolved minds to be diplomatic in those times and solve the problems and move on happily or not.
Yes I am quite the realist, and well like it or not non elaborated truth is one thing many people do not like to hear even if it is the reality of it all.