The men Jesus was speaking to were professional fishermen.  This fisherman is right in the middle of the stream where the fish live.  So are we, as fishers of men, right in the middle of the people where they live.  It's hard to see, but the fisherman pictured is wearing waders or "hip-boots" to keep the water, the basic element of the fishes' environment, away from his body.  He is willing to walk among the fish, in their environment, because he can catch more fish there.  We must be willing to walk among the people, in their various environments, because we need to get close to them to show them God's love.  As we do so, we need to ask the Holy Spirit to protect us while we are in those environments.  Some of them can be toxic to the faith of the unprotected "fishers of men."  While we are about our Father's business, fishing for  men, He will be with us, teaching us the best ways to attract people to Him for their good and for His glory, 

Fishers of Men

Matthew 4:19

"And He saith unto them, 'Follow me, and I will make you fishers of men.'" (KJV)