Portected gmes work for a while then stop. How come?

from what i know, basically the protected games ask for a magic code which is hidden in the original and does not exist in the copy. when the game asks for the code, and your copy doesnt have it, it will do a mod chip ##### and when it finds the mod chip, the psx crashes. this is what i heard anway. it might not be entirely accurate. also there are different types of this psx protection, LC1 which only #####s once right at the beggining, LC2 which does a few #####s during the game, LC3 which does alot, and finally LC4 which #####s at every load screen!