The best trick in computing is called <dfn>virtualization</dfn>. It's a very general-purpose technique for doing astonishing things. Here's how it works.

1. Take any picture.

2. Draw an outline around something in the picture.

3. Now replace either everything inside the outline, or everything outside the outline, with something totally unexpected. There is just one rule: your replacement must behave just enough like what was there before that <em>nobody on the other side of the line notices that anything has changed.</em>