Forecasting is Tricky. And Usually Wrong.

This is another entry that covers tennis, but it's not really about tennis. It's about our fallibility as forecasters when confronted with data sets that are limited.

Only close fans of the sport of tennis will be familiar with the name Gael Monfils. He had one of the greatest junior careers of any player in the history of the sport. In 2004, he had won the first three junior grand slam tournaments of the year and was attempting to join Stefan Edberg as the only junior male to ever win the junior grand slam in a calendar year. He ended up losing in the US Open, the final grand slam of the year. Even so, he put together one of best seasons in the history of junior tennis.

Surely he'd go on to be one of the greatest professional tennis players of all time as well, right?

Many analysts thought the answer to that questions was an undoubted yes. Turns out that such forecasts are shaky at best. It's usually only in hindsight that answers to such questions become obvious.

Gael went on to become one of the most dynamic players on tour, finishing in the top 50 in just his first year on tour (after starting in the high 200s). To this day, he is still one of the best shotmakers on tour and regularly finishes in the top 20 each year. He plays with a ton of creativity and panache. You never know what you're gonna get from him and he's a delight to watch for that very reason. But he never climbed to the heights analysts predicted. The highest ranking he ever achieved was #6 in the world, and that was just for a few months. His best grand slam result was a semifinal, and that has happened only twice in his 17-year career (still ongoing). To be sure, he's a better player than most people will ever be. But he was never able to achieve on the senior tour what he did on the junior tour. So what gives?

I'll offer up two explanations. One is more obvious and often applies to youth sports across the board. One is less obvious and is pretty tennis-specific.

The Obvious

The obvious reason has to do with junior sports in general. Often times, the best junior players are ones who are more physically mature and/or develop a skill set far in advance of their junior peers. In some cases, those early gains persist into the professional setting, but more often than not, the juniors that were behind the early ascender catch up and the gap in performance disappears. There are notable exceptions, of course. LeBron James comes to mind immediately as the exception to this rule. At 14, he was way more physically mature and way more skilled than any of his high school peers. His peers didn't catch up, though. Even his NBA peers didn't catch up. But for every LeBron James, there are a ton of Robert Swifts out there who never achieve success at the next level.

While Gael is no Robert Swift (he made it on the tour and has had a tremendously successful career), he appears to be one who matured quicker than his junior peers and took advantage of that skill gap, but the gap that was huge in the junior setting disappeared once he got on tour.

The Less Obvious

This is where data analysis becomes tricky. In cases like this, it's not what's in the data set (his track record in juniors tennis), it's what's not in the data set. Let me give you the names of Gael's professional peers: Djokovic, Nadal, and Federer (known nowadays as the Big Three). Let me also give you the age when each of those players turned professional: Djokovic (16), Nadal (15!), and Federer (16). You see, these three took a different route. They turned professional early, toiled in relative obscurity for a few years (Roger didn't win his first major until he was 21, even though he went on to win the most majors of all time--until Djokovic passes him), and learned a ton by getting beaten by men way older and more battle-hardened. The same thing happened in the previous generation with Pete Sampras (17) and Andre Agassi (16).

So while Gael was cleaning up in the juniors, these other three guys were getting an education in the school of hard knocks on the professional tour. Nobody can fault anyone for predicting great things for Gael and completely ignoring the Big Three. Nobody knew who they were at that time.

Forecasting is tricky business. If another great junior player comes along (and I mean great like winning multiple junior grand slams in a single year), I think it's safe to say that they'll have a great shot at earning a living playing the game they (hopefully) love. Gael has done quite nicely in that respect, earning almost $20 million dollars in prize money (and that doesn't even count endorsement deals, which often outstrip prize money by an order of magnitude).

But the more important take-away is more general: scrutinize the data you have, but beware of the data you don't have.