Say you have three hypothetical parlay legs, each with a 60% chance to win. If they're mutually independent, the chance all three win is 0.6 × 0.6 × 0.6 = 0.216, or 21.6%. There's a 78.4% chance at least one loses.
Check the whole ticket's chance to hit, not just each leg's. The multiplication shortcut requires independence. Don't assume that for a same-game parlay or multiply correlated legs this way.