The term "frame" was borrowed by pickup artists from Neuro-Linguistic Programming (NLP). The original concept goes like this: even if there is a single objective reality currently happening (e.g. It's 68 degrees and I am sitting in a classroom with 25 people listening to a lecture about physics), each person has their own individual interpretation of this reality. Different people notice different details of what's going on. Each person has their own set of memories they compare their current situation to. Each person has a slightly different emotional reaction to what's going on. The subjective interpretation of an objective reality is called "frame".
That is, everyone is looking at the same picture, but each person puts a different "frame" around it.
So frame is your interpretation of reality. The interesting thing is, when you're in a group of people you can draw others out of their reality and into yours. Whoever has the strongest frame wins.
Have you ever heard of those people who just waltzed past security and got backstage just because they acted like they belonged? Because they acted like they belonged there everyone else believed that they were supposed to be there and just let them through. That's maintaining frame.
If you wear a silly hat and think, "Man, this hat is ridiculous and makes me look stupid," then other people will think you're a loser with a stupid hat. But if you wear a ridiculous hat and think, "This hat is unique and the epitome of cool," then other people will be drawn into your reality and assume you're cool. (This is what Mystery is famous for.)
If you approach a popular kid (or hot girl) with the mindset "This person is way above me and probably has no interest in talking to me" then she will be drawn into that reality you created and think that you're a loser. If you instead approach with the mindset "I'm a cool person with interesting things to say and I don't give a fuck what anybody thinks about me" then they will be drawn into that reality and think you're a cool person. That's maintaining frame.
You have created a reality where being 16 and short is a bad thing and means your not good enough. This reality gets projected outward in your body language, tone of voice, and word choice. Other people then accept the reality that you're short and not good enough. If you instead cultivate a reality (or frame) where you're a badass regardless of your height, people will fall into that reality and accept it as true. This is where being cocky and agree and amplify help.
Edit: credit to u/untitled1