Some volume is fake. A lot of real volume is from market makers and other bots. The rest is from people. Almost all of this volume dries up in the face of volat

Some volume is fake. A lot of real volume is from market makers and other bots. The rest is from people. Almost all of this volume dries up in the face of volatility. If the market moves, people wonder if maybe the seller knows something they don't, and so they pull their limit buy orders and wait. This means slippage occurs in practice more than it would appear.