How do I explain to someone who doesn’t know anything about bitcoin that there will never be more than 21 million bitcoins?

So, I was talking to my friends parents about bitcoin today and her dad knows a little something about it but her mom knows nothing. He told me that he owns 1 whole bitcoin which surprised me and I thought was amazing. But, then her mom asked why people buy them. So, we tried to explain to her that it’s a way for people to take control of their money, and to avoid inflation because there will never be more than 21 million Bitcoin. Once they’re all mined, then no more will be added to circulation. She immediately asked “How do you know that? How do you know for 100% certain that more wont be added after those 21 million? Isn’t there some kind of ‘managing group’ that controls what happens and could potentially decide to add more?” (She’s an American businesswoman) Now, I’m not an expert but I’m also not new to bitcoin. I know that there won’t be more than 21 million bitcoins, and that they will all be mined by around 2028. I know Satoshi Nakamoto didn’t start bitcoin to make money and that its much much more than just an investment or a currency it’s a revolution. It’s a way to take the power away from the system that oppresses us. I know this, but I also don’t know how to explain to her in a way that she’d be able to understand that there’s no “managing group” that’s going to add more bitcoin to make more money after the 21 million are mined. How do I show her proof of this? via /r/Bitcoin https://bit.ly/3k6CYpp