In a $P$-$V$ indicator diagram, the net work done by a thermodynamic system during a cyclic process is equal to the area enclosed by the cycle. If the cyclic process consists of two loops of equal area but traced in opposite directions (one clockwise and one anti-clockwise), the positive work done during the clockwise loop is exactly cancelled out by the negative work done during the anti-clockwise loop. Consequently, the net work done by the system in the complete cycle is zero.