There is nothing more unknowable than the human mind.

From Life of Homer by Pseudo-Herodotus

Epigram 5

Thestorides, though men encounter many unexpected things,
There is nothing more unknowable than the human mind.

Θεστορίδης θνητοῖσιν ἀνωΐστων πολέων περ,
οὐδὲν ἀφραστότερον πέλεται νόου ἀνθρώποισιν.

And yet much of reporting today, especially political reporting, consists of imputing to opponents things supposed to be in their minds but not evidenced in reality.