When you do a fighting stance in order to prepare to break something (for example, a concrete block or wooden block), you would also say "Pil Sung!", or "must win!", but it depends on your taekwondo organization in your dojang. This "Pil Sung!" also happens when your instructor also says "gibon kyorugi" (free sparring) in some cases.
Tip: In your step test for your taekwondo belt, it is also acceptable when you hear the command "choombi" to do as before - bring your fists together at chest level, and then you do a sort of "down block" with these fists towards your belt simultaneously. This is a better "choombi" because this tells you that you have the "zanshin" to do what is next. This is extremely important to do especially before you do your "poomsae" or "palgwe". The "down block" in "choombi" needs to be tight if you do this option. Do that too loose, and it is like it is perceived that you are not having the "zanshin" before you do something, and could lead to a downgrade or a deduction a bit on your form.
