Sometimes it's fun to put things in perspective by converting stuff to "dogs years".

For example, I just found out the approximate size of surface area of our bodies. And it's not several square meters, as you might think at first. It is a lot more, because we should include all the area that is exposed to the "outside" and that includes our digestive system, lungs and urinal tract. Add all this together and you get 400 square meters. That's about the size of two basketball courts!!!

Pretty impressive on it's own, but let's look at it from the point of view of a cell of an immune system, which has to protect all this area from incoming bacteria and viruses.

First, let's conert this flat area to a sphere. That will make a sphere with radius of 5.6 meters. The size of an immune cell is 10 micrometers. Make a proportion to bring the cell to our size and the sphere's radius grows to 5.6x10^7 meters = 56000 km. That's a little more than twice the radius of Jupiter, the biggest planet in our solar system.

Now a virus to the cell is about as big as a dime to us. So there is your goal: guard the planet twice as big as jupiter from a constant rain of dimes coming from space. Sounds like fun, doesn't it?