I have recently bought a book by one of the favorite knowledgeable guy in the SharePoint world - Todd Klindt - Professional SharePoint 2013 Administration
The book is hilarious and very descent to have on the shelf if you are a SharePoint Administrator, Developer or Architect.
Here is my favorite paragraph so far, which is very metaphorical and easy memorize for someone who is new in this big and messy SharePoint World.
"Try this analogy to understand how [all] pieces work together: Web applications are the landfill. Content databases are giant dumpsters. A site collection is a big, black 50-gallon garbage bag. Webs, lists, and items are pieces of trash. Your users spend all week creating garbage, continuously stuffing it in the garbage bags, with each piece of trash occupying only one garbage bag at a time. Each garbage bag can hold only 50 gallons of trash (quotas) before it is full, after which the user has to either ask for a new garbage bag or get a bigger garbage bag. That full garbage bag is placed in a dumpster, and it is not possible to put a garbage bag in more than one dumpster without destroying it. Dumpsters are serviced only by one landfill but that landfill can handle thousands of dumpsters without issue. "