So how do you balance 18 nails on a single nail?

Monday started well then went downhill to the point where my car overheated and started steaming, back to the garage to find the radiator has another hole. Fortunately it's still under guarantee. I've a busy day tomorrow and now have to try and work with a not very efficient public transport system. Yes, I know 70% of the population have to make this system work and I'm behaving like a spoilt brat!
I also know there are fewer than 18 nails in this photograph but I grabbed a handful for the photo. You'll have to wait until I take a photograph of the rather simple solution, unless you've done this exercise before? Point of the exercise is that things often seem impossible until you do it.