Reader's Block

Last night, a friend mentioned that there was a book that was given to him a while back that he started to read and had to put it down - it was too much for him at the time - then he picked it up again in a year and it was great.  Ive had a similar experience with A Testament of Devotion by Thomas Kelly, Life Together by Dietrich Bonhoeffer, and No Man Is an Island by Thomas Merton, though I haven't yet gotten to the "picked it up again" part.  I wonder if it's better for me to try and force myself through a difficult book, or give myself time...