I personally think thats just a myth. Heres why.

Most people don't know how to inhale, so when they smoke they just suck it in and don't inhale, it just chills in there mouth, which leads to people not getting high. My friend who I thought we smoked with a few times smoked last weekend and I noticed he didn't inhale, so I show him how and he winded up passing out and getting wrecked. It seems to be just a myth.