Earlier quoted context omitted.
If the full time wage can't result in a decent living (housing, food, medical expenses, clothes, feed and clothe a kid or two, and put away a little on the side) then it clearly is too little. Edit: Check out https://livingwage.mit.edu/ for examples based on real-world data.
If the job is unskilled (i.e. you can train the next person to do it in less than one hour) and you have several people standing in line to take it if the person doing it, quits; then the current wage is clearly enough. It is just like the price of the meal. If it costs more than people are willing to pay, then it is too expensive; regardless of what you personally think it should cost.
If the person doing it (and the role can make or break the business) quits on short notice, then the current wage is clearly not enough.