If you're old, when we were kids we needed encyclopedias to read anything (esp. nonfiction.) You can't understand a book if you don't know any of its references

If you're old, when we were kids we needed encyclopedias to read anything (esp. nonfiction.) You can't understand a book if you don't know any of its references, and you're not going to go to the library to look up all of them. All you had is what you'd stored up in your head, and the encyclopedias in the basement. They were nice to kill idle time following references, just like Wikipedia is now, but they were essential for reading nonfiction at home.