Sheep have no good way to defend themselves against predators. They are also stupid.  Easily startled, they tend to bolt, without thinking about where.  Commonly, the rest of the flock instinctively follows suit, frequently stampeding toward greater danger.  A few years back, USA Today reported a huge loss of sheep in turkey that began as one decided to jump off a cliff.  The shepherds, who had left to have breakfast, watched helplessly from a distance as more than a thousand followed.  450 died. Sheep are stupid.   

So are humans.  That’s why the Bible calls us sheep.  Isaiah said, 

All we like sheep have gone astray; we have turned—every one—to his own way…   (Isaiah 53:6a)

And when Jesus “…saw the crowds, he had compassion for them, because they were harassed and helpless, like sheep without a shepherd.”  (Matthew 9:36b)

We have been designed by God to be connected to Him by means of His Holy Spirit.  Without that living connection, we are easily confused, frightened, influenced to stampede toward danger and defeated.  Like sheep.  But, God loved us and arranged to reconnect us through the work of His Son, Jesus.  He is the Good Shepherd.  

The Lord is my shepherd; I shall not want… He restores my soul.  (Psalm 23:1 & 3a)

For you were straying like sheep, but have now returned to the Shepherd and Overseer of your souls.  (1 Peter 2:25)