Shin Shin Shin Gan is an expression you may hear during your training in Japan. It can be translated as the heart and the eyes of the divine. Shin 神 (kami, sacred, divine) Shin 心 (heart) Shin 神 Gan 眼 (eyes). Shin Shin Shin Gan. 
Your eyes can be easily deceived. In fact, all of our limited senses can be easily deceived. Just think of the magician that makes a tiger appear in an empty box. The tiger is not appearing out of the air, it is skillfully hidden in the unseen compartments of the box or stage. But we are very surprised. We pay a lot of money to see magicians fool our eyes and senses. Sometimes it is pleasant to be fooled and sometimes not so pleasant. The ladyboys in Thailand love fooling the love hungry soldiers coming in off the ships! Maybe it is best they never know the truth!
It reminds me of a story. In the honbu dojo in Noda, Hatsumi Sensei has a picture in the dojo of a woman putting on makeup. He once told me it represents Yamato Takeru No Mikoto, a Japanese legendary prince of the Yamato Dynasty. To kill a very powerful enemy, he once dressed as a woman maid attendant at a drinking party and successfully assassinated his opponent. 
Even a picture in the dojo fooled me. You may even be looking at something directly for many many years and not know what it truly is!
A true ninja cultivates the heart and eyes of the divine. Not seeing with just the eyes, not listening with just the ears, not tasting with just the tongue, not smelling with just the nose, not feeling with just the hands. If you don`t cultivate yourself, you will be fooled over and over. You will continue to chose poorly and find yourself at the point of your opponent`s blade. This is true for choosing teachers as well, if you choose wisely, you will have a wonderful experience. Choose poorly, and you will find yourself on a dark and perilous road. But don`t worry, in the end, both will die!
Those that have cultivated the heart and eyes of the divine are like sunflowers. They don`t choose any more. They just move. When the sun rises in the easy, they turn their faces to the light, when the light moves to the west, they turn their faces westward. Moving with the light, they don`t choose, they just move in the direction of light naturally, without thought. A true ninja is like a sunflower, it is hard to judge him because we are always fooled choosing this or that, but he is always moving naturally with the light.