The work of reason produces monsters

Poincaré, “Mathematical definitions and education,” 1906, in Science and Method, translated by Francis Maitland:

Logic sometimes breeds monsters. For half a century there has been springing up a host of weird functions, which seem to strive to have as little resemblance as possible to honest functions that are of some use. No more continuity, or else continuity but no derivatives, etc. More than this, from the point of view of logic, it is these strange functions that are the most general; those that are met without being looked for no longer appear as more than a particular case, and they have only quite a little corner left them.

Cf. Goya’s El sueño de la razón produce monstruoscirca 1799: