Why “Trinity” for God existence in most of religion?

I wonder why in most of religion “Trinity” is associated with god existence like for example in Christianity Trinity of “father , son and holy spirit”, and similarly in Hinduism Trinity of “brahma, vishnu and mahesh”. Why the Godly existence have Threeness, or to say have with three different nature or property.

First of all, God, in general, considered to be ultimate reality the whole sole one with none other at par to him.

Therefor if we go with this oneness of god as ultimate reality there arises a conundrum, as the very existence of one comes in doubt without a second, so for one to be one there need to be two otherwise this one for an existential entity is not more but a zero.

So when you talk about ultimate reality you comes with zero, one and second. Zero is the existence of nothing and for some thing to be some thing you need two — one and second.

So there need to be “two” substantive reality for something, to compliment each other existence.

Now interestingly here Zero is ultimate or beyond reach, never come into existential realm of any second perception and for the sake of that it has to become one with a second. So its a son who incarnate with a holy spirit never the father, father is beyond the reach or having a meta-existence.