After a series of strong earnings reports, including a second quarter that exceeded analyst expectations, Apple (NASDAQ:AAPL) stock is trading near its all-time high. Apple is far and away the largest company in the world, and the biggest component of the S&P 500.

While there are plenty of reasons to believe Apple could be headed even higher, its possible that the iPhone maker may have hit its peak. Below are three scenarios that, should they come to pass, would be likely to harm Apple shareholders.

Apple's growth could slow

Apple's first- and second-quarter earnings reports of this fiscal year were the largest in the company's history, due almost entirely to extraordinary iPhone sales. In total, Apple sold 135.7 million iPhones from the beginning of last October through the end of March. That's a massive number, and it may be difficult to top.

The iPhone 6 and iPhone 6 Plus were arguably the most significant upgrades in the product's history, finally giving iPhone owners something they had wanted for years: a larger screen. The iPhone 6 may have pulled forward some demand that otherwise would've taken place in 2015 or 2016. And while Apple will certainly be able to improve on the iPhone -- perhaps adding additional features like Force Touch or wireless charging -- it may be unable to spark another massive upgrade cycle.

Apple could still generate billions this year, and for many years hence, but if its growth slows or even reverses, its multiple could contract, and shares could trade lower.

The Apple Watch could flop

At this point, Apple is largely a one-product business. The iPhone generates roughly 70% of its revenue (even more if one includes indirect, but highly derivative, revenue sources like app store sales). The Mac business has been reliable but not growing, and the iPad's recent performance has been quite disappointing, especially given the once lofty expectations many had for Apple's tablet.

So far, that hasn't really mattered as the iPhone is an incredible product with great margins and loyal customers. So long as that's the case, Apple can continue to generate billions and return capital to shareholders. But many investors want more: They expect Apple to unveil entirely new, successful products in different categories.

Apple's most recent product, the Apple Watch, could become Apple's next megahit. At least for now, its total addressable market is limited to the number of iPhones in use, but if it manages to sell millions and generate strong growth, investors will be confident in Apple's continuing ability to innovate and develop new products.

But what if Apple Watch fails? Unfortunately, it will be difficult to discern the relative success (or failure) of the Apple Watch, because Apple has already said it doesn't plan to release specific figures. But if demand cools, if surveys show relatively low levels of penetration and consumer interest, if sales become common and Apple Watch sightings become rare, investors may begin to doubt Apple's ability to innovate. That doubt could take a toll on Apple's stock.

The iPhone business could struggle

With so much of its revenue coming from one product, Apple's financial performance -- and its shares -- would likely take a significant hit if its iPhone business began to unravel.

The iPhone is arguably the best product in its class, with a number of significant advantages over the competition, including more and better apps, build quality, customer support, a tight-knit ecosystem that encourages customers to stay, and strong carrier relationships. These advantages will be difficult for Apple's competition to overcome, but they are not insurmountable. Samsung's latest smartphone, the Galaxy S6, received rave reviews and includes an optional feature Apple can't match: a curved screen. Other Android OEMs, such as Xiaomi, are showing both rapid growth and promise in emerging markets. Radical new experiments, like Project Ara, could eventually undermine the current smartphone business model that Apple's business remains dependent on.

Just a decade ago, the handset business was dominated by a number of entrenched, seemingly invulnerable firms: Nokia, BlackBerry and Motorola. Apple's iPhone slowly overtook, then eventually destroyed, their businesses almost entirely. It may be unlikely, but Apple remains vulnerable to disruptive competition.