Michael Coslo wrote:

At the risk of being both a dullard and messing up all the fun, does
not every destructive interference have to be balanced by a constructive
interference, which in turn leads to a condition of "Okey dokey?"

A canceled wave needs a reinforced wave, and then nothing is lost,
nothing is gained.

Not quite, but close. It's ok to have two waves that cancel at one place
but go their separate ways at others without reinforcing. Any
combination of canceled, reinforced, and independent waves is ok as long
as the energy all adds up to the amount put into the system.

The purveyors of these contrived questions have never been able to
explain how they create these exquisite co-traveling canceled waves
without also creating those nagging reinforced or non-canceled waves.
Since it requires magic to create them, it should be no surprise that it
requires magic to explain what happens to the energy once the magical
canceling waves have been conjured up.

Roy Lewallen, W7EL