Who in the hell said it's supposed to be fair?

A couple of weeks ago one of my kids blurted out, "That's not fair", a statement that literally brought me to a dead stop.  Who in the hell said it's supposed to be fair?  Granted I phrased my question a bit different at the time, but the sentiment was exactly the same.  When did life become about fairness?  Is there a 11th commandment stating, "Though shall be fair"?  Life is not fair, we have all heard that at some point and they are right, but is life supposed to be fair.  What exactly does fair mean?  My definition of fair most likely differs from yours, so how do we reach what is fair.

In theory it sounds good for all to be fair, but the varying definition of the word Fair would never leave us all feeling that everything is fair.

Definition of the word Fair from Merriam-Webster:

1: pleasing to the eye or mind especially because of fresh, charming, or flawless quality

2: superficially pleasing : specious <she trusted his fair promises>

3a : clean, pure <fair sparkling water> b : clear, legible

4: not stormy or foul : fine <fair weather>

5: ample <a fair estate>

6a : marked by impartiality and honesty : free from self-interest, prejudice, or favoritism <a very fair person to do business with> b (1) : conforming with the established rules : allowed (2) : consonant with merit or importance : due <a fair share> c : open to legitimate pursuit, attack, or ridicule <fair game>

7a : promising, likely <in a fair way to win> b : favorable to a ship's course <a fair wind>

8archaic : free of obstacles

9: not dark <fair skin>

10a : sufficient but not ample : adequate <a fair understanding of the work> b : moderately numerous, large, or significant <takes a fair amount of time>

11: being such to the utmost : utter <a fair treat to watch him — New Republic>

— fair·ness noun

What are you teaching your children when it comes to the word fair?  Life is not fair and nor is it supposed to be, but life is beautiful.  At least that's what my children hear from me.  My children earn their own money and from the monies they earn they can buy anything they wish.  Some peoples definition of fairness would take the money from my children and give it to others, as in our tax system.  In all actuality of our tax system we really just take more from some people, disguised as fairness, but it seldom ends up going to other people.  Instead we get more bloated government agencies.  If I were to take something from my children on the grounds of fairness, then I would indeed be teaching them life is not fair.  More so, I would be teaching them to not work hard.

Teaching your kids about being fair can lead to some very dark places, as such I urge you to fully explore your thoughts about being fair before teaching this to your children.

Who in the hell said it's supposed to be fair?