It was me who brought this up in a discussion with Yori. My main point was that I'd think it would be harder, the more difficult it is for a person to engage in solely mental exercises. Many people are distracted, short attention span, their minds are, for lack of a better word, blunted. Intelligence isn't exactly what I meant.
I said incapable, but what I mean was that really, if you possess the sort of mind that will bore quickly or give up on a fully mental task every single time.... even if you possess the faculties required for that task, you are in effect incapable.
The reason I sa