Facing a long putt with a lot of break, you know that getting down in two is usually just fine. But you're really seeing the line on this one, so you step in thinking you could make it. As soon as you hit the putt, you realize it's way short. There's a term for what you just did: "falling in love with the line." You concentrated so hard on the break, you neglected the speed.
When I was a kid, my brother and I would practice putting for hours while we waited to get on a packed golf course. We learned by trial and error that distance control is more important than direction on long putts. Even the ones with a lot of break—the putts we hit from one end of the practice green to the other.
Phil Mickelson, who I worked with for years, has a great drill for pace. He places three balls 40 feet from a hole, three at 50 and three at 60. From 40 feet, all three putts need to finish within a club-length of the hole. Then he moves to 50 feet, then 60. The balls can finish left or right—the distance is the key. Give it a try.