re: Help me understand this horse track bet

When you box a trifecta, you're making 6 different bets. Say you're boxing the 1, 2 & 3 horses.

You're making the following $2 bets:
1,2,3
1,3,2
2,3,1
2,1,3
3,1,2
3,2,1

One of these $2 bets won and had about 4-1 odds, hence your $8 payout.

In the future, if you're betting favorites, try not boxing them. Or, try an exacta box where you're only picking win and place, but only making 2 bets ($4).