A person reading a new book for pleasure is like a tourist traveling to a new place  The reader reads, just as the tourist travels, to enlarge understanding rather than simply to acquire information
Thus, it is better to read fewer books and spend more time on each rather than to quickly read as many as one can, just as it is better to travel to fewer places and spend more time in each rather than to spend a small amount of time in many different places
Tourists gain much more understanding of a place once they have spent several days at that place than they do in their first few days there.