Well, if a circuit is operating at high-frequencies and radiates signals (either due to an intentional antenna connected to the circuit or due to stray inductances)....the electro-magnetic signals thus generated are capable of inducing a voltage (commensurate with the original signal) in any stray inductance (e.g. a long wire piece) and thus interfere with the normal operation of this victim circuit.
A good example can be seen if you bring your cell phone close to your monitor and dial a number.
Hope this helps.