My mom once said she did something where she gave me something and gave my sister nothing. She realized I would share with my sister so she could be happy too.
Communism is an ideology. At birth, you are totally devoid of any ideology. Your brain has only the basics of life support capabilities at birth. The only thing your brain is doing is developing.
Someone had to teach you the concept of communist ideology.
That’s “how”.
I never knew it but I was. I always had a sense that making others work for your profit is wrong. I also believed that being communal was a good thing because I had a sister I always shared with. I was shamed for being sister-like when I was 5.