Why do thorns and thistles exist?
Because Adam "hearkened unto the voice of his wife."
And unto Adam he said, Because thou hast hearkened unto the voice of thy wife, and hast eaten of the tree,
of which I commanded thee, saying, Thou shalt not eat of it:
cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life.
Thorns also and thistles shall it bring forth. Genesis 3:17