why so?

Why so?
Last day in our daily class discussion we came to a strange point of our talk.It was about the pair of marriage.
As it is belived in our religion (islam) that pairs are made Or created in heaven before anyone's birth.But a But a person after marrying why they diwas(talaak) each other due to some reason?
Is person's attributes are more than Allah?of course they are not.but how person is able to break the pair which Allah have created in Heaven <- A real point to ponder.



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