Thought experiments—these experiments that we perform only in our imagination, like Einstein's falling elevator—have played an important role in the establishment of quantum physics. Yet, their legitimacy was—and still is—contentious. How is the validity of an experiment conducted in the "laboratory of our mind" to be ascertained? Such worries too often arise from a misunderstanding as to the nature of thought experiments, which are commonly understood and used as mere rhetorical devices, inductive argument, or self-contained models. But in the eyes of those influenced by Leonard Nelson, thought experiments should rather be understood as small, but important elements of the broader dialectic arguments necessary for the establishment and development of physical theories. Far from being irrefutable proofs for the Nelsonians, thought experiments must be constantly revisited, transformed, and repurposed as our understanding of nature deepens. More importantly, as the debate between Werner Heisenberg , Karl Popper , and Grete Hermann on the microscope experiment demonstrates, it is this very flexibility that enables thought experiments to contribute to our understanding of nature even when they fail.