a) There's a limited supply of bitcoins b) The amount of bitcoin you get decreases as more are made c) The larger the network the more it costs to make a bitcoi

a) There's a limited supply of bitcoins b) The amount of bitcoin you get decreases as more are made c) The larger the network the more it costs to make a bitcoin d) Some bitcoin are deleted forever, accidentally. So a) Bitcoins become harder to make, and b) The total possible number of Bitcoins goes down.