There are a few common misconceptions about soccer (called "football" everywhere other than in the United States) goalkeepers. Let's take a look at these and then examine how things really are.
Misconception #1 - Being a soccer goalie is easy because you don't have to run around very much.
People who aren't familiar with the game will see all the players running around on the field and then see the goalies who are "just standing there" and assume it must be easy.
The truth is that goalies have to be 100% aware of what is going on at all times. While it may not be as physically demanding as the other position, they do still need to be able to move around a lot -- and quickly -- especially if the ball is equidistant from the goalie and an opposing player and they are both running for it.
A goalkeeper also has to be precisely aware of where he is on the field, and know where the goal is without needing to look back and see it. Taking your eyes off the ball for even a split second can result confusion which can lead to the other team scoring.