Intent is intended with the eyes. I know that it is so. Yet, just like you, I can't pinpoint what it is I know. Sorcerers resolve this particular difficulty by accepting something extremely obvious: human beings are infinitely more complex and mysterious than our wildest fantasies.
All I can say is that the eyes do it. I don't know how, but they do it. They summon intent with something indefinable that they have, something in their shine. Sorcerers say that intent is experienced with the eyes, not with the reason.