No one knows what he is doing ...

No one knows what he is doing so long as he is acting rightly; but of what is wrong one is always conscious.
No one knows what he is doing so long as he is acting rightly; but of what is wrong one is always conscious.

Quotes from the same author

Knowing is not enough; we must apply. Willing is not enough; we must do.
Just trust yourself, then you will know how to live.
The really unhappy person is the one who leaves undone what they can do, and starts doing what they don't understand; no wonder they come to grief.
What is not started today is never finished tomorrow.
A man sees in the world what he carries in his heart.