To illustrate, let’s play a game. We each put in a dollar, and whoever wins a coin flip gets the two dollars. Completely fair, even odds, right? We’ll play until one of us decides to stop or someone runs out of money.
I’ll start with $1000 and you start with $10. Let’s see how it turns out.
If it helps, picture a graph where the bottom axis is number of coin flips and the Y axis is the amount each player is up or down in total. Each flip can move the graph by $1, up or down randomly. So it’s going to bounce a little, because it’s random. Some bounces will be bigger than others.
The house can offer you completely fair odds and still take your money just fine.