For things to happen in failure in a Double Cards Activation is a backfire or repercussion of damage, weakening, or any ailments. To get a Backfire/Repercussion in a Double Cards Activation is to put together non-compatible cards, like Water Body and Fire Body, the two Boosts/Ability will clash due to opposite forces, but it can work for them join together, but without enough Will and Power, they cannot join.