To throw a coin into a wishing well tells much about us humans:
Desires as wishes can only be acknowledged in exchange for something of worth.
Some traditions suggest that if the coin lands heads up, the wish would be granted. Otherwise not. We believe we can have certainty about whether our wishes will be met.
The wishing well tells of our fear of scarcity and our need for certainty.
Both of those, I would wish to wish away.