Well, if you're actively starving, then obviously you won't get enough. And if you're only eating e.g. rice, then you'd likely be satiated before you have enough of certain amino acids. But aside from that, it's quite difficult to not get enough protein, as carb-heavy food also contains protein.

I can recommend listening to this podcast/video for a more detailed explanation: https://zoe.com/learn/podcast-should-i-eat-more-protein