Truly, man has no excuse for not noticing God.
The fool hath said in his heart, [There is] no God. They are corrupt, they have done abominable works, [there is] none that doeth good. - Psalms 14:1
And when he putteth forth his own sheep, he goeth before them, and the sheep follow him: for they know his voice.
And a stranger will they not follow, but will flee from him: for they know not the voice of strangers. - John 10:3-5
Isn't that a beautiful line?
"...the voice of strangers..."