In class, while no-contact sparring a much larger adult, a young teenager may block attacks and score points with ease. The teen then thinks he or she would actually be able to defend effectively against an adult attacker. The same holds true for a woman sparring a man or a man sparring a larger, stronger man. I am hit the most and injured the most when I am sparring a teenager or a woman, regardless of their size. I am not a very large man but I am reasonably quick and very powerful, so, when sparring teenagers or women everything I do is less powerful and less quick because I do not want to hurt them accidentally.
They, on the other hand, think that because they are blocking my attacks or getting through with a technique that they could actually defend against my attacks and hurt me if I were a real attacker. I am a power blocker who was taught that blocks should be performed as if they were attacks, so sometimes I block their attacks with power or use power attacks to let them know that I have been allowing them to be ineffective and that they are not as good as they believe they are. The same holds true for me when I spar bigger and better fighters; they sometimes let me know they are just playing with me as a cat plays with a mouse before the kill.
Taekwondo training involves learning and perfecting Taekwondo techniques but it also involves strength building, and mind and body hardening. It does not matter how perfectly you perform a punch or kick, if it does not hurt the attacker, the attacker will keep attacking. The only thing that impresses a bad guy is pain—preferably his or her pain. You cannot inflect pain if your strength is weak, your body is not hard, and are you are not mentally capable of inflecting pain or injury. Likewise, you cannot deal with your own pain if your strength is weak, your body is not hard, are you are not mentally capable of dealing with your pain or injury.