Acoustic resonance is the increased tendency for an object to vibrate at a particular frequency that it’s configured for. For example, a guitar string tuned to E will vibrate on its own when it “hears” another E – you don’t have to strike the first string in order for it to move.
Harmonics are multiples of a base, or fundamental, frequency. The “A” note is known to be 440Hz. Another note that plays with A that is a multiple of 440Hz is a harmonic – 220Hz, 110Hz, 880Hz.
In music, resonance and harmonics are used to create complicated orchestras and symphonies that defeat our understanding of nature. We can always describe a musical note as a wave, but no book in science truly understands the effect that music has on us.
My point is – we don’t have to be in similar frequencies to understand each other, nor do we have to wait for someone else to take action – we play our string so others’ start moving on its own.