I've been asking people and looking at some of their history of posts and I see it all the time, most people here are just not eating enough.
Insufficient protein happens when people don't eat enough. It's almost impossible to get your calorie fill and not get complete protein.
If you don't eat enough, you're not going to get enough amino acids, not enough fatty acids, not enough vitamins, not enough minerals, and most importantly, not enough fuel (calories).
Use cronometer to do a diet sample and you'll see what I mean. Even on a vegan diet, it's really easy to get enough protein as long as you reach your calorie minimums.