Sin = Selfishness

i have been thinking about how we as humans have a sinful nature. the more i thought about sin and what is considered a sin the more rapidly i came to the conclusion that all sin spawn from the same thing, selfishness. the essence of sin is nothing but selfishness. instead of having ten commandments we could just have one. don't be selfish. i think the only reason God gave moses the ten commandments was to break down selfishness and give examples of it. so that people couldn't question what was selfish and what wasn't. what other choice did God have? we as humans constantly try to rationalize situations to justify how what we are doing or what is happening isn't just for our own good but the good of others, or at least not effecting anybody else. for any sinful act i can think of i can make an argument on how it is a selfish act.