Step 1: Recall what makes a well artesian.
An artesian well draws from a confined aquifer, where the water layer is trapped between two impermeable layers.
Step 2: Think about the state of the water inside.
Because the aquifer is sealed and recharge areas are usually higher up, the water inside is squeezed and held under pressure.
Step 3: See why the well flows on its own.
Once a well is drilled into this pressurized layer, that pressure pushes water up and out without any pump, gravity pull, or capillary action needed.
\[ \boxed{\text{Pressure}} \]