Don't you feel a certain sense of accomplishment after finishing a book or a novel? I certainly do. Perhaps more so over the years as my pile of unread books starts to accumulate, and there's also a number of books which I've started reading but never got to finish.
The easiest thing for me on the other hand is to purchase a book. There's excitement when you acquire it and as long as the book remains unread, the possibilities are endless. This is a double-edged sword however. Sometimes, the book falls short of the hype and you only realize that by the time you read the last page. There are some books however that are well worth the praise and a rare few when they exceed it.
I don't think I have problems starting on a new book. I do have problems though continuing to read it until you reach the end. Either real life gets in the way, my concentration lapses, or there's something more appealing to do at the time (such as writing!). But it also varies depending on the author's discourse. Some books are easier to read or are more interesting than others.