Why wires strands during pre-stressing work

Question

What is the reason that all wires or strands should be stressed at the same time while doing pre-stressing work, if more than one wire or strand is taken in the same duct?

Answer 1

If wires or strands are stressed separately within the same duct, then those stressed strand or wires will bear against those unstressed ones and trap them. That is why; the friction of the trapped wires is will be more than required.