“Nothing is so firmly believed as that which we least know.”
—Michel Eyquem De Montaigne, French writer, statesman, father of Modern Skepticism (1533-1590)
We still don’t know exactly how people learn language. It seems like it is through comprehensible input. There is good evidence for that. It also seems like TPRS/TCI is at least one of the best ways to teach, but when better methods come along, we must be ready to accept them and not take our pet theories as dogma.