Jacking may be necessary during construction. If two objects are in contact the forces between them are equal and opposite. If an object is not accelerating in a given direction, the sum of the forces on it in that direction is zero. The minimum force needed to support the weight W of an object is W, obtained when the object is supported by a vertical pillar or a vertical cable. Supporting a weight W by means of a force applied anywhere but at the object requires a total force greater than W. Even if the supporting forces are parallel with the weight, there is the weight of the intermediate members to consider.
Tension members can be much thinner than compression members.
The rope that held up the bust while it was being lifted and positioned was very much thinner than the thinnest pillar that would safely support it. The force at the bottom of one leg is the weight of one leg plus the weight of one quarter of the deck and one quarter of the cables. Each cable at the top has to support the weight of itself plus one quarter of the deck. Because of the shallow angle of the cable the force in it is very much greater than the force in the leg, yet the leg is huge compared with the cable. This is because a strut can buckle, whereas a cable remains straight under any applied force, until it breaks.