A common reason for missing short putts is deceleration of the putterhead through impact. The main reason this happens is because the golfer takes too big of a backswing and then has to slow down through impact to avoid hitting the putt too hard.
Here’s a good putting acceleration drill to help you avoid decelerating during those short putts:
1. Set up to a two foot putt.
2. Without taking a backswing, just push the ball firmly into the hole.
3. Repeat pushing the ball into the hole five times and then practice some three foot putts while using a normal stroke.
After doing this putting acceleration drill, you will find that three footers are much easier!