Early investors in Intuitive Surgical (NASDAQ:ISRG) have enjoyed one heck of a profitable run. The company's stock is up more than 7,650% since its IPO in 2000. That's a strong enough performance to turn a few thousand dollars into a retirement nest egg. More recently, the company's winning streak extended into 2016 with shares rising more than 15%.

While there are plenty of reasons to believe that Intuitive's winning streak can continue, shareholders (like me) always need to keep an eye on the bear case, too. With that in mind, here's a look at three reasons to believe that Intuitive's stock could fall from here.

Image source: Intuitive Surgical.

1. International payers limit adoption

While Intuitive reported that total da Vinci systems sales volume increased 9% during 2016, the company didn't experience growth across the board. In fact, that figure includes a 12% decline in system placements in Europe.

Management explained that the weakness came from countries where the company lacked local clinical and economic data that supports the use of robotic surgery. While Intuitive has plenty of data available from in the U.S., many foreign governments want to see the company produce country-specific data before they would be willing to open up their wallets.

To help rectify this situation, the company is investing in local studies with the hope of proving that robotic surgery provides both financial and clinical benefits. However, there's no guarantee that the company can succeed, especially since this issue has been raised before. That makes it possible that sales in some international markets could remain weak.

2. Competition finally heats up

Image Source: TransEnterix.

One big reason that Intuitive Surgical has been so successful in the past is that it has had the robotic surgery market all to itself for years. However, that could finally be set to change in 2017. TransEnterix (NYSEMKT:TRXC), a small-cap robotic surgery company, is finally ready to submit its Senhance Surgery system for FDA approval. The company believes that the device will be in regulator's hands "in early 2017," which gives it a chance to be on the market before year end.

While TransEnterix is dealing with plenty of its own problems, it would be a mistake for investors to overlook the competition. The Senhance system claims several advantages over the da Vinci system, so it is possible that a few hospitals systems would be willing to give it a hard look. If true, then Intuitive could be forced to turn to pricing as a way to compete, which wouldn't be great for profits.

3. The valuation is too high

While Intuitive's dominant market position and enormous growth runway have allowed its stock to almost always trade at a premium valuation, the company is now quite mature. That means it will be hard replicating past growth rates.

Market watchers appear to agree with that thesis. Current projects call for long-term earnings growth of just 9% over the next five years. That's quite a bit below the 13% EPS growth that it put up over the past five years.

While slowing growth is to be expected, Intuitive's valuation continues to look quite rich.

ISRG PE Ratio (TTM) Chart

ISRG PE Ratio (TTM) data by YCharts

If Intuitive fails to exceed the market's growth expectations, then its trailing P/E ratio of 35 could be viewed as far too high. If true, Intuitive's stock could be in for a nasty fall.

I'm still bullish

Despite all of these potential negatives, I remain quite bullish about the company's long-term prospects. In addition, I'm a firm believer that winners tend to keep on winning, so I have no plans to trim my position anytime soon.