English As we have already answered above, if the outcome hits the middle, then the player profits from both bets, in other words, you get a very good profit. In case of a defeat, the winnings will only be received by one of the bets.
A positive middle means that the player profits in any case if the profit is based on only one bet. In practice, such middles can be very rare and narrow, and sometimes it makes no sense to pursue them just because they are positive.
A negative middle means that if the player misses the middle and only one of the bets wins, the player is left with a small loss. This is acceptable for those who want to make middles wider and increase the probability to won both bets and make up for any possible disadvantages.