February 17, 2010 — If a book is worth reading, it's worth buying too.
If you're reading a book primarily to gain value from it(as opposed to reading it for pleasure) you should always buy it unless it's a bad book.
The amount of value you can get from a book varies wildly. Most books are worthless. Some can change your life. For simplicity, let's say the value you can derive from any one book varies from 1 cent to $100,000(there are many, many more worthless books than there are of the really valuable kind).
The cost however, does not vary as much. Books rarely cost more than $100, and generally average to about $15.
You shouldn't read a book that you think will offer you less than $100 in value. Time could be better spent reading more important books.
So let's assume you never read a book that gives you less than $100 in value. Thus, the cost of a physical copy of the book is at most 15% (using the $15 average price) of the value gained.
Would owning that book help you extract 15% more from it? It nearly always will. When you own a book, you can take it anywhere. You can mark it up. You can flip quickly through the pages. You can bookmark it. You can easily share it with a friend and then dicuss it. If these things don't help you get 15% more out of that book, I'd be very surprised.
Where it gets even more certain, is when you read a really valuable book--say a book offering $1,000 of value. Now you'd only need to get 1.5% more out of that book.
The investment in that case is a no brainer.