A fixed block does not give a gain in work, it only allows you to change the line of its action.

A fixed block does not give a gain in work, it only allows you to change the line of its action. How to explain this phenomenon from the point of view of the rule of moments.

The block is stationary in a normal situation is symmetrical, therefore the points of application of forces are at equal distances from the center of the block, therefore, the shoulders are equal, the Block is at rest, therefore the sum of the moments of forces is zero, which means that the forces must be equal in modulus.