"Boards don't hit back." That is a famous line from the Bruce Lee flick, Enter the Dragon. He was expressing the thought that while many martial artists demonstrate their prowess by breaking boards, it doesn't prove anything because the boards never return the favor. How easy would a fight be if the other guy just stood in place, or better still was kept from moving by four or six of your best friends?
I'm not sure you could call that a fight. Or ethical. I'm pretty sure it is not even entertaining. I'm thinking that if you have to have a half dozen buddies hold your opponent in place in order to crack a guy's rib, then maybe what you're doing isn't self defense. Maybe it's assault, or extortion, or an offer he can't refuse - if you catch my drift.
I trained for years with a good fellow who attempted a tournament break to punch through three boards with his right hand, while breaking three more with his left elbow, simultaneously. One set of boards in front, the other behind him. At the tournament he managed to mess up his fist with his punch and bruise his upper arm from the elbow to his shoulder. He was out of commission for weeks. The lesson here is that it only takes a little mistake; insufficient power, loss of focus, or poor timing - and the boards will hit back.
As practiced in Tang Soo Do, board breaking, especially at the Black Belt and tournament levels is supposed to represent two concepts, and demonstrate two skills. We require that the artist break three sets of boards, to represent being attacked by three assailants at the same time.
Il Kyuck Pil Sal, is a Korean phrase that we translate into "one technique to finish", i.e. I hit the attacker one time and the fight is done. Period. Board breaking represents two concepts; first that a practitioner has techniques that when executed would end a fight immediately, and secondly that the practitioner can do three of these different techniques either simultaneously or in very rapid succession.
The skills required to pull this off can be grouped into two broad categories. First, the practitioner must be able to execute the techniques with such precision and power as to be effective (i.e. you have to connect with the right spot on the boards with sufficient power to break them). Secondly, the practitioner must be aware of his surroundings. Bad guys rarely stand in a line and let you take them out one at a time.
So while it is true that boards don't hit back (hopefully), the bad guys shouldn't either. If your techniques are well honed, your focus, concentration, awareness, and technical skill are right, "Bad guys don't hit back."