In Reid Hoffman’s excellent book, Blitzscaling: The Lightning-Fast Path to Building Massively Valuable Companies, he looks at what it takes to supercharge a company’s growth and dominate an industry. Of course, dominating industries leads to massive stock gains.

One of the companies that Hoffman covers is Alphabet (NASDAQ:GOOG, NASDAQ:GOOGL). He notes: “At Google, Larry Page and Sergey Brin built great search algorithms, but it was their innovations to the search engine business model – specifically, considering relevance and performance when displaying advertisements rather than simply renting space to the highest bidder – that drove their massive success.”

Hoffman’s assessment is spot-on. As of now, GOOGL stock is worth a staggering $757 billion.

Yet maintaining success is never easy. The tech market is full of examples of epic implosions. Take a look at what happened to Nokia (NYSE:NOK) and BlackBerry (NYSE:BB). Not long ago, they seemed to be unbeatable leaders in the lucrative mobile phone market.

So what might go wrong for GOOGL stock? Where are its vulnerabilities? Well, interestingly enough, the main threats to GOOGL may not necessarily be from scrappy startups. Instead, the real problem for GOOGL stock could ultimately come from other huge tech companies, such as Amazon.com (NASDAQ:AMZN).

The Threat to Alphabet Stock From Amazon

Keep in mind that AMZN has taken a low-profile approach to its move into the online ad business. But nowadays, AMZN’s efforts in that area are getting too hard to hide. The fact is that Amazon’s online ad business is becoming a major source of its growth.

According to research from eMarketer, Amazon’s ad revenues are projected to double this year to $5.83 billion. And based on analysis from Cowen & Co, the e-commerce giant’s ad business could ultimately be worth as much as $28.4 billion. If that forecast – which does seem reasonable – proves accurate, then GOOGL stock could easily come under a great deal of pressure.

AMZN has a unique advantage: its massive e-commerce platform. When people visit the site or its other apps and platforms, they are generally focused on making purchases. That is certainly an attractive attribute for any advertiser. By comparison, when a user does a Google search, he or she may have other reasons to do so i.e. to learn something or to be entertained.

AMZN also has tremendous amounts of purchase data on its customers. This will likely be a major competitive advantage for AMZN, as the data should enable advertisers to enjoy much higher conversion rates.

Other Risks Facing Alphabet Stock

AMZN is not the only factor that could weigh on GOOGL stock. The company is also facing some other major challenges. For example, its privacy policies and alleged anticompetitive practices are being scrutinized. The European Union has already levied a $5 billion fine against the company because of its actions involving its Android operating system.

But this may be just the beginning. GOOGL is also involved in litigation in the EU regarding the company’s potential violations of the bloc’s General Data Protection Regulation (GDPR) act.

Interestingly enough, monetary damages may not be the real problem for Alphabet and GOOGL stock. Rather, the major harm to Alphabet stock is likely to come from restrictions on the company’s use of data, which could ultimately make it much more difficult for GOOGL to monetize its platforms in Europe.

The Bottom Line on GOOGL Stock

Over the years, GOOGL has been trying to become involved in businesses other than digital ads. Yet its results have been mixed. Just look at the company’s cloud segment. Despite making substantial investments in its cloud business, GOOGL has not been able to gain much traction in the cloud space, as it has just 3.3% of the market. Conversely, AMZN has a 51.8% share and Microsoft’s (NASDAQ:MSFT) share is 13.3%. Note that GOOGL recently hired a new executive to head its cloud unit.

Now for the most part, the major risks facing GOOGL stock will not have a material impact on the stock for some time. And GOOGL still has some major advantages, including a huge cash position as well as multiple, highly successful assets like YouTube, Gmail, Maps, Chrome, Android and Play. But if GOOGL wants to continue to thrive, the company should start acting more aggressively, and it should do so as soon as possible.

Tom Taulli is the author of High-Profit IPO Strategies, All About Commodities and All About Short Selling. Follow him on Twitter at @ttaulli. As of this writing, he did not hold a position in any of the aforementioned securities.