This commercial makes it look like your drill instructor will tell you not to quit.
I won't say that wouldn't happen, but it's pretty unlikely. That is, they don't inspire you through encouragement and positive reinforcement, but through the opposite of those things. You're 1,000 times more likely to hear, "I hope you drown."
This one shows recruits lining up on the Yellow Footprints, and responding to a command with "Yes Sir!" You only say "yes" in response to a question. When you're told to do something, it's, "Aye aye Sir." This might seem like a small issue, but it's one more mistake will get a recruit treated extremely harshly for hours. A recruiting commercial is a little early to be setting a guy up for special murder time (that's what we call corrective training).
In the same commercial, one recruit knocks down the other in a pugil stick fight, and then helps him up. They wouldn't actually be allowed to help each other up. In fact, they can't stop beating each other until specifically instructed. This is just a rumor, but I heard you get extra money for killing the other guy.
They say Marines fuck Yeti. I don't know where that came from, but it's not true. Yeti itself is a myth, first of all. And to say we fuck it is obviously intentional slander. And the numbers don't work out. If Yetis did exist, there would be way fewer of them than there are Marines, and they're in remote locations. The logistics would be a nightmare.