Glasersfeld E. von (1995) Sensory experience, abstraction, and teaching. In: Steffe L. P. & Gale J. (eds.) Constructivism in education. Erlbaum, Hillsdale: 369–383. https://cepa.info/1461
Excerpt: In short, understanding is something all of us have to build up for ourselves. In this respect, understanding is not unlike a physical skill. For instance, if beginners stand on skis for the first time, it is quite useless to tell them what they should do to go down a slope. They have two unwieldy contraptions strapped to their feet, that make them lose their balance at the least provocation. They are paralyzed and quite unable to do anything. This state is similar to the state students get into when they are faced with arithmetical symbols for the first time (and the paralysis immobilizes them again when they have to face algebra)