What is an Experience Point?

I first encountered the below thoughts about XP in some random blog or reddit post.  Sorry to the person who's idea it is, I don't remember who you are.

1 Experience Point (XP) represents the amount you learn in a day of going about your craft.  If you take in to account days of rest and other distractions, we can hand wave that to about 300xp per year.

With about 40 years of working life for a human, you can assume they earn about 12,000 xp over their productive years.  What level this may equate to may vary depending on game edition and class.

Lets take a caravan guard.  Growing up, they were a zero level NPC, as a caravan guard they are likely a member of the Fighter class.  Lets also assume we are using a classic D&D XP chart (2,000 at first level, doubling thereafter).  Our caravan guard, presuming they live, will likely make it to 4th level (maybe 5th if he kills his share of bandits and gets XP for those)

Note: if you use gold for XP, I would not count their pay as XP, I would just use the 1xp per day as an abstraction of their earning power.  If they got some bonuses or shares of spoils at some point, I would award bonus XP for same. (if for some reason you wanted to simulated the life of a caravan guard)

A Dwarf weaponsmith would likely have 300 or so productive years.  This put them in the neighborhood of 7-8th level.  An Elven sage could likely make it to 9th level. So one could see how such long lived races would gain a reputation for great skill in particular areas, even if the traditional adventuring party only has a few pips difference in ability.

These numbers also help give an idea of how accomplished (What level) your "normal" people are at a given point in their career.   Taking about 5 year or so to make it to 2nd level.  This (very roughly) aligns with the idea that it takes about 10,000 hours to become skilled at something.

Admittedly, all of this is very abstract, but it does help give an idea of what your average schmo is accomplishing and help fill out your world with something more than 0 level NPCs waiting to be slain by house-cats.