I am not convinced. Yesterday whilst I was killing time before my flight I was reading a section of AC Grayling's Wittgenstein: A Very Short Introduction where he sought to get across a point about different 'language games'. I must have read and re-read those few paragraphs about six times struggling to get the meaning, and I still don't quite grasp it (maybe I'll have a cuppa and another go later). I would put money on it that AC Grayling is smarter than I am, and that he is quite capable of explaining things clearly. So I have to assume I am (or was being) a bit dense.
What's more, I became aware that in trying to get my hands on the meaning of the passage I was trying to find something familiar in it. In other words I think I was trying to understand the concept by sort of sub-dividing it by something I do already 'know'. Of course it's partly mental laziness. In fact someone I posed the original question to said that yes you can grasp anything, provided that you want to. I am sure that your attitude must play a role but don't quite agree. My view is that it's about familiarity. It's hard learning new things, it's much easier sort of 'spotting' concepts you already get. People seem to derive great enjoyment from doing well what they know how to do. Maybe the same process is at work when we try to understand something - it's more enjoyable to think about it in a way we already know how to think. We enjoy the familiarity.
In epistemology one of the big theoretical divides is between "knowledge that" and "knowledge how". Here's how the Wiki article on epistemology explains it:
For example: in mathematics, it is known that 2 + 2 = 4, but there is also knowing how to add two numbers. Many (but not all) philosophers thus think there is an important distinction between "knowing that" and "knowing how", with epistemology primarily interested in the former. This distinction is recognised linguistically in many languages, though not in modern English except as dialect (see verbs "ken" and "wit" in the Shorter Oxford Dictionary).
I guess in this instance "knowledge that" is what I describe above as "familiar". So what surprises me is that even in an area like philosophy "knowledge that", or maybe our desire for "knowledge that", can play a big role. And it leads me to question whether maybe a lot of what we take to be "knowledge how" is actually "knowledge that". Because it is very familiar to us we think it is more conceptual than it actually is.
The caveat is of course that maybe this is just the way my mind operates, maybe other people approach knowledge differently. Indeed I do think that people have differing tastes for certain "forms" of concepts, and that these can be developed. But I think generally we are more similar than we are different and as such others must suffer from the same failings that I do.