Inner Eye
Some say that there are three parts of human beings, intellectual, emotional, and spiritual.
They differ from each other, and with experiencing one you can't experience the other.
For example, with intellect, you can't explain how does it feel to fall in love. Intellect can understand one's behavior, but in the feeling of love, the person would need to go through that feeling to understand how it feels to be in love.
There are some that claim that certain knowledge can't be obtained by the intellect but rather by spiritual experience. The person would need to go through some spiritual experience to gain that spiritual understanding, to obtain that inner, spiritual eye.