If you catch the ball little bit thin, you can still get a shot out of it. The ball will go fairly straight, and while you won't get all the distance you expected, it's still a playable shot. Hit it fat, and it's all over. Put your 5-iron back in the bag, take ten steps, and take out your 6-iron. That's not how to have fun on the golf course, and there's no reason you should have to play that way.
The several causes of hitting fat all have easy cures. The first thing to check is ball position. If you play the ball too far forward, your swing bottoms out before it gets to the ball. Just play the the ball farther back. The center of your stance is a good spot.
Hitting fat can be caused by releasing your wrist set too early. In the worst cases, the release happens simultaneously with the start of the downswing. In any event, when the wrists are released too early, the club and arms form a straight line.
If they stayed straight, the ball could still be struck, but without much power. Hitting fat will occur if the wrists continue to release, throwing the club head down to the ground instead of through the ball.
The cure is to keep your wrists oriented as they are at least until they have gotten down to hip level, when gravity and the buildup of momentum force them to release naturally into the ball. That way, the club-arm lever will stay the right length.
Another cause of hitting fat is leaving the weight on the right side after the downswing has started. The weight will shift somewhat to the right on the backswing, but only into the inside of the right foot.
If the weight shifts to the top of the foot, or even worse, to the outside of the right foot, there is a real danger that you won't be able to get it back to the left. The hub of the swing has now shifted to the right, and the swing will bottom out before it gets to the ball.
Making sure when you swing back that the right leg does not sway to the side, but stays in place. Think of your right leg as a fixed post around which your swing revolves. The turning motion of the downswing will move your weight back to the left and bring the club right back to the ball.
A fourth cause of hitting fat is in the conception of the downswing. Yes, the club has to fall down several feet from the top of the backswing to get to the ball, but this is not chopping wood. It's propelling a golf ball forward. Your conception of the swing must be centered on the six inches before and after impact, when the club is moving forward.
A final cure can be to think of hitting the front of the ball instead of the back. Think that the ball is transparent to the club and solid only along the leading edge. Aim for the leading edge, and your club will still be traveling downward as it strikes the ball. And that's not fat, that's money.