The discovery of the alphabet will create forgetfulness in...

The discovery of the alphabet will create forgetfulness in the learners’ souls, because they will not use their memories; they will trust to the external written characters and not remember of themselves… You give your disciples not truth but only the semblance of truth; they will be heroes of many things, and will have learned nothing; they will appear to be omniscient and will generally know nothing.

— Plato, from Phaedrus, predicting that written language would make us all dumber. A fun quote to reference next time you encounter someone arguing the same about the internet.