Because you can rig the answer if it's just one person. But if two of you use the method from the post, and both commit to your answers before revealing them, then neither of you can rig it.

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IAmBroom 9 hours ago | parent [-]

That assumes "rigging" is the only non-random component. There's also unintentional bias; when asked to name a random number between 1-100, multiples of ten are underrepresented due to our bias.

	▲	jstanley 9 hours ago \| parent [-]
		It solves the rigging problem, it doesn't necessarily make claims as to whether that is the only problem that exists.