My databases professor at my university once brought up Jim Gray's data latency analogy to illustrate the costs of using different types of storage. Basically it goes something like this:

Using a register is like interacting with information in your own brain, using an L1 cache is like walking to a bookshelf in the room you're in, using an L2 cache is like walking across campus, using RAM is like going to Sacramento (we were in Berkeley), hitting the disk is like going to Pluto, and using tape drives is like going to Andromeda.

I never fully registered the consequences of hitting disk until then.