It's what we do.

I've just rebuilt the magneto on my mate's 650 Norton, set the ignition timing and need to fit new gaskets.
  He always asks me how I know how to do jobs like this.
When you're an apprentice and your bike breaks down on the way home, you push it for several miles and get stuck in to fix it, to get back to work, the next morning.
  It's a really fast way to learn about the workings of the internal combustion engine and anything else that's fastened to it !