According to Osho, 'Know thyself' stays within rational dialogue and keeps a subtle knower intact; at truth’s peak there is no dialogue, and even the ‘I’ disappears. ‘Let go thyself’ points beyond knowing—to being, surrender and silence—where the I–thou coin dissolves. First become integrated and free; in that discovery, selfhood drops by itself.
Trying to know yourself keeps a 'you' in place; letting go drops that 'you' so only quiet, free awareness remains.