All of a sudden, I realise why GOD exists.

It's because deep down in heart, in soul, human beings are eavil. We have desires, and with all the desires, good and evil can varies between each other so fast, that no one can make judgement.

So acient brilliant people meet GOD when trying to find their peace in heart, and they decide to leave their soul to GOD and let GOD regulate their mind and behaviour.

So it doesn't matter GOD exsits or not, or even you can say that GOD is you and everyone, but stands at a higher level of life.