It's an overall pattern and on a continuum so you may be able to "concentrate" on some things but overall, others notice you have a hard time concentrating. One "should" be able to concentrate on anything they want to concentrate on, whether they like it or not.

My husband, for example, has had to study finance and investment over many years now to make sure our retirement is secure. He has no interest in those subjects but reads many many books (I would be hard pressed to do that and I like the subject!) and financial experts online, subscribes to expert sites, etc.

How well do you do on reading comprehension tests? I use to read 5+ books a week but once applied to work in a library and when they quizzed me on recent books I'd read and authors names, tell them what it was about, etc., I wasn't very good on the details!