karmic encounters

Like balls on a billiards table, when two particles run into each other, they bounce apart. In contrast, when two waves meet, they pass right through each other

(click on the photo)

As the animation shows, when two waves overlap they add up to form a larger wave (reinforcement) :-)

BUT PLEASE NOTE... : they can also cancel out to form nothing at all (cancellation), or partially cancel to make a more complex waveform.
This is called interference :-(