A properly weighted die

Okay, normally, sure. But what if I cross my fingers and kick my heels and rub my lucky clover?

That's unlikely on a D20. They're almost all polished in rock tumblers which leaves edges rounded to random radiuses and faces all different sizes

That's true of all sizes but matters more on the dice with more faces

On most dice rolling a 1 or 20 or 12 indicates that that number is probably more likely than others to come up

Some dice are worse than others, reportedly the TSR red box d20s were egg shaped with 1 and 20 on the ends making those numbers highly unlikely