Several years ago a major university conducted a study on barracudas and minnows. The students wanted to see what would happen when a barracuda and minnows were put into the same fish tank. The results were pretty much determined before the experiment even began lunch for the barracuda!
Then the students wanted to see how the barracuda and minnows (more minnows) would react when put back in the fish tank but this time a pane of glass was placed in the middle of the fish tank preventing the barracuda from feasting on the new batch of minnows. Wouldn’t  you know it, that barracuda kept slamming into the glass time and time again trying to get to the minnows. Eventually the barracuda realized he couldn’t get to the minnows and stopped trying.
At this point the students wanted to see what would happen if they took out the
pane of glass separating the barracuda from the minnows. So they did.
Do you know what happened? Nothing! The barracuda had become conditioned not to approach the glass, he learned it hurt. And for the remainder of the experiment the barracuda never crossed the imaginary line of the glass.
How many of us as Christians have become discouraged, hurt, or dejected after our repeated attempts to witness to a friend or family member. So much so that now we don’t even approach the glass (referring to the barracuda)? Like the barracuda we have become conditioned through Satan’s lies.