pierce, penetrate, brace
毌 centers on the idea of passing through or holding firm: piercing, penetrating, or bracing something. The brace sense likely extends from the idea of something that goes through and secures.
毌 is an ancient pictograph of a string or rod passing through an object, representing piercing or threading. The modern form retains the basic shape of a line through a frame.
Picture a vertical line piercing through a box-like frame: the line goes straight through, penetrating and bracing the structure.
For カン, imagine a can being pierced by a sharp rod: can -> カン, and the rod penetrates the metal.