stolen from alanna_liadon
Quoted from http://www.shamusyoung.com/twentysidedtale/?p=1223
"The Truth About 20-Sided Dice:
Thereare a limited number of “twenties” in any given d20. That is, no matterhow many times you roll a d20, you cannot roll another twenty once thesupply has run out. These twenties can only be replenished by rolling acorresponding one with the same die. Thus every gamer is duty-bound toprotect their supply of good rolls. If a friend rolls a twenty usingyour die, not only have they stolen your good roll, but they havedoomed you to the extra one required to replenish the twenty.
Someplayers get excited when they roll several twenties in a row,concluding the dice are “hot”. Don’t make this blunder! This is likedriving your car for 400 miles without gassing up, and then concludingthat your car is a perpetual motion machine. After a few good rolls,pass the die off to an unwitting companion and let them charge it upfor you.
Statisticians have known about this behavior for years.They call it “the probability seesaw”. Unlike the bell-shaped curve, inthe seesaw system the odds of rolling high or low is directlyproportional to what has been rolled in the past. They usually pretendthis isn’t true. If a statistician hands you a die insisting that “anygiven roll has the same odds of rolling a one or a twenty”, it meanshe’s handing you a depleted die in the hopes of taking advantage ofyou. Don’t fall for it!
Now the secret is yours. Please put this knowledge to good use."
"The Truth About 20-Sided Dice:
Thereare a limited number of “twenties” in any given d20. That is, no matterhow many times you roll a d20, you cannot roll another twenty once thesupply has run out. These twenties can only be replenished by rolling acorresponding one with the same die. Thus every gamer is duty-bound toprotect their supply of good rolls. If a friend rolls a twenty usingyour die, not only have they stolen your good roll, but they havedoomed you to the extra one required to replenish the twenty.
Someplayers get excited when they roll several twenties in a row,concluding the dice are “hot”. Don’t make this blunder! This is likedriving your car for 400 miles without gassing up, and then concludingthat your car is a perpetual motion machine. After a few good rolls,pass the die off to an unwitting companion and let them charge it upfor you.
Statisticians have known about this behavior for years.They call it “the probability seesaw”. Unlike the bell-shaped curve, inthe seesaw system the odds of rolling high or low is directlyproportional to what has been rolled in the past. They usually pretendthis isn’t true. If a statistician hands you a die insisting that “anygiven roll has the same odds of rolling a one or a twenty”, it meanshe’s handing you a depleted die in the hopes of taking advantage ofyou. Don’t fall for it!
Now the secret is yours. Please put this knowledge to good use."