First of all, I know this (or, similar) question has been discussed previously here. But the discussion there couldn't help me completely getting rid of my confusion, hence this attempt.
In any radioactive sample of a particular element all the atoms involved in that accumulation of sample are obviously seem to be indistinguishable in every aspect. Then why all the atoms don't start decaying at the same time?
In practice we obviously know that they don't disintegrate simultaneously and hence my question arises that what is that x-factor that differentiates between the atom which decays first than the others?