1) They Come Off Their Line For No Reason
Goalkeepers come off their line to narrow the angle. This makes the target smaller for the shooter. But you don't have to watch much football to see keepers charging off their line when the shooter is being closed down by defenders, is in a poor shooting position, or both.
Watch this, from Hearts keeper Jamie MacDonald:
Suarez is being pushed wide, and by the time he shoots, his angle is very narrow. He's on his left foot as well, so there's no danger he can bend it around MacDonald to his far post. His defender has done his job; if he just stands up big and strong at his near post, he makes the save. But as soon as we see MacDonald in the frame, he's already at the edge of his six-yard-box, perhaps anticipating Suarez will beat his defender and come straight to goal. When this doesn't happen, he's caught moving out and to his right as the shot comes in. He gets in the dreaded no man's land, where he's not close enough to Suarez to spread himself and block any shot, but too close to give himself any reaction time.
The Lesson: If the striker is at a tight angle or is being closed down by a defender, hold your line, stand up, and react to the shot. Standing up means it takes a quality finish to beat you. Getting caught in no man's land means the easiest little toe poke can result in a goal.
2) They Don't Trust Their Wall at Free Kicks
We all know how this works: the wall covers the near post, the keeper covers the far post. You may be 99% sure the shooter is going to go over the wall, but if you anticipate that and he beats you to the far post, the side you've just abandoned, you've got nobody but yourself to blame.
Remember that it's not easy for the shooter to get the ball over the wall and then back under the crossbar. Even when they do manage it, it will usually lack pace, and you'll have time to get across to deal with it. It's much simpler to avoid the wall and shoot at the far post, especially if the keeper has abandoned it. Make the shooter do the hard thing.
3) They Get Bogged Down in Superstitions
Magic isn't real. If you play poorly or well, it's down to you. Your energy is much better spent in other ways.
I realize that lots of top pros are superstitious. That doesn't mean it isn't a crutch, because it is, or that they wouldn't be every bit as good without the superstitions, because they would be. Copy their work ethic and concentration, not their superstitions.