Myth 1: All backs MUST be able to make 20-meter spiral passes off either hand.

Nonsense! In any game you can count on one hand the number of passes (other than scrumhalf passes) that travel more than 10 meters. Of course, backs must be able to pass and particularly to pass flat but more than anything they must know when to pass.

Myth 2. Backs should spread themselves across the field to "create space". 

This myth is particularly pervasive and destructive. Two fast-hands, 10-meter miss passes will give any wing more running space than he (usually) knows what to do with. AND anyway, how often in a game is a wing strike actually on?  My guess is 5 times or less.  "Get the ball to the wings!" is the usual cry of spectators who are dazzled by spectacle rather than efficiency in attack and should not be pandered to.  

Myth 3. Wings are the prime attackers. (See also above.)

This myth is particularly dangerous since it is so clearly incorrect. The prime attackers in the backline are the three interior backs -- plus the fullback. Wings are, in fact, part of the defensive unit that includes the fullback. The fact that they don't or won't understand this is the reason that your 10 and 8 spend so much of their time covering when they should be setting up for the counter attack. Wings' role in attack is very specific and they should be used selectively.
This myth is all the more dangerous because it serves to confuse the interior backs about their roles.

Myth 4. What you need in the backs are terrific individual players.

No! What you need are terrific support players.

Myth 5. The "loop" play works because it brings in an extra man and the opposition don't know whom to tackle.

Wrong! Of course an "extra" man gives the defense something more to worry about but the reason the loop play works is because the looping player arrives at pace. You only have to draw it out to see that the looping player has to move faster than the inside man to get into position and it is this extra speed that creates the strike. This is true also of fullback insertion plays -- the poor fullback HAS to accelerate to catch up and paradoxically it is this acceleration that often gives him the break.   (Which, by the way, all leads to the question, "If the inserted player CAN accelerate into position to take the pass does this mean that the ball carrier is not moving at full speed?" The answer to this is, obviously, "Yes!"  But then we must ask why the ball carrier is not moving at full speed.)

Myth 6. A back must avoid (i.e. go away from) his oppo. to beat him.

All you have to do is to watch a reasonably speedy back slice through a bunch of static forwards with hardly a hand laid on him to realize that this can't be true. What a back carrying the ball must do is "fix" his oppo. in place -- usually by running straight at him. Once the tackler is rendered static the ball carrier's chances of a break are greatly enhanced plus he has created space for a slip pass into the place where the tackler would/should (?) have been. There is nothing that flankers and drifting centers like better than opportunities to "cross the T" provided by ball carriers angling off. Destroy this myth and you'll never have to hear "Run straight!" again.

Myth 7. "Breaking the line" means man beating a man.

It doesn't -- or at least it mostly doesn't. Breaking the line means getting a ball carrier behind the defense however you achieve it and is more often a collective exercise than an individual one.  

Myth 8. The stand-off, out half or whatever you call him is the general and, as such, should not be used as a striker.

  Maybe this was once true but no longer. Every successful 10 must have the ability and indeed the need to make a running attack.  Especially as he is the back closest to the opposition's most vulnerable point -- the "seam" between backs and forwards.

Myth 9. It is always better to pass than be tackled.

Here it's the "always" that's the problem. It is always better to keep possession and, if possible, maintain the impetus of the attack than to pass to a covered man. The reason the "always" has crept in is that backs in support notoriously distance themselves from the ball carrier, drawing their oppos with them. If your support is, as it should be, close enough for a quick pop or slip pass or even just a smuggled ball a break or half-break can often be made even in close traffic.

Myth 10. A back's role in support is over once the ball carrier is tackled.

Absolutely not!  Being first in to recover the ball on the ground or, failing that, aggressively setting up the ruck is a key part of continuity and backs must take a lead in this. The forwards already think you're a wuss but why confirm it! Get in there and win the ball!

Myth 11. When you break through tuck the ball under one arm and go!

Inside the oppositions 40 meters yes, perhaps, but being in a position to exploit a break and send in a mate for an easy score by fixing the opposition’s last man is usually the difference between 5 for us and a turnover, lost in contact.

Myth 12. The corner flags are there to mark the corners of the playing area.

Not at all! The corner flags are there only to remind wingers where they are supposed to attack