Have you even been in your car stopped at a stoplight with your foot on the brake? You know you are stopped, and yet, when the car next to you rolls back a few inches, for a split second, you think you are moving and push harder on the break. This is way feints and fakes work; you make your opponent react to a perceived, but false, threat.
Feints and fakes are useful in drawing out an opponent who always lets you attack first. The opponent may be tricked into attacking by offering him or her a target in a way that is not obvious, such as slightly raising your guard to invite a mid level attack.
Since fakes are uncompleted techniques, to be effective, they must look like genuine attacks, such as raising the knee and setting up for a front kick, so opponent will react by lowering his or her guard. To complete the strategy, you then attack an undefended high target. Alternatively, after raising your knee for a middle front kick to drop the opponent's guard, you could change the kick to a roundhouse to the unguarded high section. When using punching techniques, fake with one hand and then strike with the other, or fake with one hand and then attack with same hand.