If you've played or watched any amount of golf in your life, you've almost certainly heard someone say something to the effect of, "At least I missed on the pro side."
And if you don't know what the "pro side" is in golf, then you were probably confused. Well, let us explain what the "pro side" is and what it means for golfers -- pros and amateurs.
Missing on the pro side
In golf, missing on the pro side means missing a breaking putt on the side of the hole where the break starts, not where the break ends.
For example, if a putt breaks from left-to-right, then missing on the "pro side" means missing on the left side of the cup, not the right side. In this example, missing on the right side would mean missing on the "amateur side."
The opposite would be true for a right-to-left break on a putt: The right side is the "pro side" miss and the left side is the "amateur side" miss.
On relatively straight putts, there is no pro side or amateur side. It just goes in or it doesn't.
Why is it called the pro side?
The pro side is referred to as that because of the belief that a putt which misses on that side at least had a chance of going in the hole. A putt that misses on the pro side -- also called the "high side" -- could conceivably go in if the golfer putted the ball with better speed. A putt that misses on the amateur side -- also called the "low side" -- meant the golfer didn't play enough break and, according to popular belief, would never be able to make the putt.
The myth of the pro side
The notion that the high side is the pro side is a myth.
Two factors go into making a putt: line and speed. Both have to match up for a putt to go in the hole. However, on any putt, there's a variety of minutely-different speed and line combinations that could result in a made putt.
Missing on the high side means playing either too much speed or too much break. Missing on the low side means either playing not enough break or not enough speed. Which is better than the other? They're both misses.
Even if you want to insist the high side is the pro side, great putters miss on both sides of the cup. They also miss short and long sometimes, right in line with the cup. Putting is difficult, and better putters are able to make adjustments with their line-and-speed reads. Poor putters typically are poor at reading greens, meaning they won't translate what might be a fine stroke to a made putt.
If you want to be a great putter, do two things: miss less and, when you do miss, miss near the cup -- on the low side or the high side.