In consulting firms and companies, the thesis has often been put forward that technological developments can be represented by simple S-shaped curves. According to this theory, the cumulative research and development expenditures invested in a technology and the technological performance, measured by a technological performance metric, are supposed to exhibit an S-shaped relationship. This work critically examines the extent to which this is true. Both the verification based on a specially designed model of technological development, the considerations within a case study on superconductivity, and the analysis of patent applications and publications as indicators of S-curves lead to the conclusion that S-curves are not suitable for representing and explaining technological developments.