Persistence is established by common parlance
As we have already explained before, persistence implies committing a particular sin again and again or different types of sins, without regretting it or seeking forgiveness for it. Or to commit different types of sins together. But the number of times a person must commit the sin that makes it ‘persistent’ depends upon how it is generally considered. So, there is no fixed standard because of the wide variations in smaller sins and their proximity to greater sins. Some smaller sins become great only by committing them thrice and some more than Three times and some in less than that. It all depends upon what is generally accepted.