The NES was known for having a lot of difficult games. Ninja Gaiden, Castlevania, and others punished gamers long before Dark Souls became the “popular” difficult game of the modern gaming generation. The difference, though, is that most games back then actually gave you some sort of chance, and that failure definitely felt like your fault instead of the game just being incredibly cheap, as Dark Souls and many other modern “difficult” games today are.
Contra was as close as games back then got to truly insane, cheap difficulty.
It was still very much a playable game, but many points in the game involved a very difficult to avoid spread of enemy placement and bullets that made it very difficult, if not impossible to avoid at times. To make things worse, the game had the one hit, one death style of gameplay, and it gave you a grand total of three (!) lives to make your run. Sure, there were continues, but with only three lives and limited continues, you couldn’t make much use of them.
Fortunately for the sanity of gamers, there was the Konami Code. Pressing Up, Up, Down, Down, Left, Right, Left, Right, B, A at the title screen gave you thirty lives instead of just three, making completing the game a much more doable goal. (Many people report that the code includes the Start button at the end of the code; this is not actually part of the code and is just used to start the game, proven by the fact you can hit Select before Start to choose two-player mode.) This code was used in one form or the other in many games and even other uses such as on websites or in applications after Contra, making it one of the most famous videogame codes in existence.