In a newly unearthed interview, Hideo Kojima shared that he faced near universal resistance against his idea for Metal Gear until he pointed out the iconic exclamation point that lets players know they've been spotted by the enemy. (Try not to hear the sound challenge, go!)
Talking to Nice Games way back in 1999 (available now due to the great work over at Shmuplations), Kojima explained how the kernel that would eventually become Metal Gear was Konami's desire to make a "war game." Kojima said that a team of veteran Konami developers had an idea for a war game and then scrapped it, and then came up with another, and scrapped that, and so and, so forth. Eventually the project fell into Kojima's hands, and he put forth an idea for an "escape game" inspired by the 1963 movie The Great Escape, but was told "'There's no games like that'."
