If you buy one gallon of milk, price is a constant.
But if you want to buy 1000 gallons, you first empty out the cheapest store A at price X. Then store B is emptied out at price (X+dx). Prices rise as you buy more.
Same for BTC.
1) precisely how supply or demand shocks change prices by adding new [price, quantity] pairs
2) how markets truly are emergent phenomena, outside the control of any one actor
3) how many business concepts change once you treat prices as variables