I am fairly happy with the meaning of this phrase but am wondering are there any good theories on where it originated?
I have one theory that makes sense in an Irish context. Dotted around Ireland we have holy wells. These wells were originally pagan but became Christianised.
The story is that if you visit the holy well you will have good luck if you honour the well or perform some kind of ritual.
I imagine that some souls thought they could keep returning to the well to garner more and more good luck. This isn't sustainable and eventually the well will dry up for them metaphorically.
I have a friend who frequents such a well and I think he is overdoing it! His language is "I must go back to the well now".
I am not sure if I think the origin is the obvious one about a water well: you wouldn't go back to a water well --- you would just use it regularly I think.
Any opinions are welcome and thank you.