Adam sinned and fell.  Humans still sin and still fall.  “Death passed from Adam to all in that all sinned”  (Romans 5:12).  The Tree of Life was not enough for Adam.  This Tree was a type of Him Who was to come.  Adam walked away from it, and we have walked away from it.  Every time we fail to follow the teachings of Jesus we fall, because we are walking away from the Tree of Life.  Following Him and His teaching brings the Life He came to give us.  When we live in solidarity with Him we will stand.  

“Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned.” Romans 5:12 (NASB)