Harmonics produced by stringed instruments can indeed have an amplitude greater than the fundamental frequency. This phenomenon occurs when the string is restrained at specific points, such as the middle, allowing the second harmonic to resonate more strongly. Additionally, bowing or plucking the string at certain locations can enhance the amplitude of specific harmonics. These techniques exploit the physics of standing waves and resonance. Understanding these principles allows musicians to achieve a richer sound by emphasizing higher harmonics.