I would no sooner underline a passage in a book I am reading than I would dog-ear a page to mark my place. At least that's how I am now, a stickler for keeping books in pristine condition. Leafing through some books I read back in the 1970s and '80s recently, I was surprised to find that I underlined quite a bit back in those days.
All this underscoring makes these books less valuable for resale than they might otherwise have been, but it certainly does make it easier to find the good parts in these old books, or at least the parts I thought were good when I read them. Here are some passages I underlined, all of them having something to do with children:
My son was born in 1972, so I'm sure I read these books and underlined these passages with him in mind. I certainly don't need these books any longer and I was tempted to get rid of at least some of them, but those underscored lines make the books harder to part with. And with all that underlining, who would want to buy them?