It is hard to get enough protein on a vegetarian diet or Plant protein does not contain all essential amino acids and you have to carefully combine plant foods in your diet in order to get the "right" protein.
Protein is one of the three macronutrients of our dietary requirement. They are nitrogen containing compounds of which amino acids are the basic structural unit; amino acids are small organic compounds containing at least one amino group and an organic acid group. Proteins are the most abundant organic compound of the body much more than fats and carbohydrates. About 65% of the total body protein lies in the skeletal muscles. There are more than 50,000 different proteins in our bodies. These are all made from about 22 different amino acids. Our body can synthesize 14 of these 22 amino acids, we cannot make 8 of them, and these 8 must come from food. These 8 are called the essential amino acids. Sometimes we cannot synthesize other amino acids and therefore they too must come from diet. Our body requires not protein itself but amino acids. We break down all protein we eat into its constituent amino acids and absorb them that way. This is the reason why diabetics can't take insulin orally, as insulin is peptide harmone and it would be broken down into its amino acid constituents as it passes through the digestive tract. It doesn't matter what the source of the amino acid is, beef, egg or soybean. We really need to get the 8 essential amino acids from diet and it doesn't matter where they come from.