• Positive Middle: the normal outcomes still give a profit or at least no loss, and hitting the middle pays much more. These are rare.
• Negative Middle: the normal outcomes give a small loss, say $3, while hitting the middle pays much more, say $90.

A negative Middle is a calculated risk, not a locked margin. Before betting, check what happens if only Bet 1 wins, only Bet 2 wins and both win, and decide whether the possible loss is acceptable.

Read more: How Middles Work