When talking amplifiers, I sometimes get the impression that whole groups of electronics hobbyists and engineering students have been brainwashed by endlessly hearing and repeating the mantra “Gain-bandwidth product is a constant.” Hearing this statement so often, they actually start to believe this is a universal truth.
I was reminded of this once again some time ago, when I saw a video on the otherwise excellent YouTube channel “w2aew.” At around minute 2:23, the host says “...for a single-pole response, the product of the DC-gain and the bandwidth is constant":