Suppose you are going to play chess against two people: one person is really good, one person is quite bad. You are going to play three games and you always have to alternate your opponents. Namely, you can either choose to play the opponents in the order
Good, Bad, Good,
or you can play the opponents in the order
Bad, Good, Bad.
Which of these two play sequences gives you the optimal chance of winning two consecutive games?
You can approach this problem using probability and tree diagrams. However a little logic goes a long way.
Specifically, in order to win two consecutive games you have to win the middle game. Thus, it is best to put your weaker opponent in the middle. Thus, Good, Bad, Good is the best strategy.
An alternative way of also seeing this answer it that you're probably going to lose against the good player, so the Good, Bad, Good play order gives you two chances to win against the good player, rather than just one.
If you want a bit more rigor then Ben has created a YouTube video solution.
Alternatively, you could try three player chess and team up with the weak player to beat the good player. But that might be considered cheating...