I received this question from a group I'm a member of on facebook, and whilst I'm not sure how appropriate it is for me to ask this, I'm going to anyway.
Anyway the poster said this
Marking. I love this mechanic from 4e. It makes defenders able to do their job. But friends of mine who are used to primarily playing earlier editions (2e, 3e) would struggle to understand it, and never use it when playing defenders. Is there any way to simplify it?
I'd also wonder if this is the case with other people they know who have migrated from earlier editions, and how they help them adapt.