Why tamp your grinded Coffee before inserting your piston into your Espressomachine?
The art of tamping is not rocketscience. For a double shot of Espresso you grind 14 grams of beans into the piston. In fact that is just a small amount of Coffee. When you don’t divide the Coffee equally in your piston then the water, that is pushed under high pressure trough the piston, will search a way with low resistance. The result is a poor cup of Coffee because the water could not contact all the Coffee in the piston.
Check this short instructionfilm for the right way of tamping: