In a discussion with his friend Philipp Frank in Prague, Einstein expressed his concerns about a trend in physics that suggested some phenomena, due to their unobservable nature, should not be considered real. This new approach troubled him, as it seemed to undermine the principles of scientific inquiry.

Frank reminded Einstein that this very idea had its origins in Einstein's own work from 1905. In a humorous retort, Einstein acknowledged that while he had introduced the concept, he believed it was time to move beyond it, implying that even good ideas can become outdated or misinterpreted if repeated too often.