It is all about balance

With shelf space being a "fixed" quantity, pushing collections into the long tail requires balance. By lengthening the tail in each library that would require shortening the head. There is only so much physical space, so the more that libraries play into the niche's, the less they can provide for the masses. But is a niche in one library a part of the mass in another? The best way for libraries to effectively represent the entire tail is the use of consortium's and inter library loans. Page 148 of Anderson's book says it all about the balance between heads and tails:

" If you just have the products at the Head, you find that very quickly your customers want more and you can't offer it. If you just have the products at the Tail, you find that customers have no idea where to start. They're unable to get traction in the marketplace because everything you're offering is unfamiliar to them. The importance of offering the stuff at both the Head and the Tail is that you can start in the world that customers already know: familiar products that tap into and define a space."

Libraries have to work hard at balancing the head and tail as well as locating for their patron's things they cannot immediately provide. Then they can tap into both the Head and the Tail.