One instructor I had insisted that I always write down my clearances etc, and only attempt the readback once the clearance was written down. And the readback came not from what I remembered, but instead came from what I had written down. That way I know that what I have written down is correct and can be refered to as often as necessary. It was one of the best pieces of advice I've ever got, and doesn't really take much time
Some pilots don't do that ? They must be incredibly intelligent and able. I have to write it all down otherwise I forget bits of it, and later during the freda check I refer back to the QNH I wrote down.
On the other hand it may explain why there is 2s pause before I read back, but I'd hate to not have it down in black and white.