Throughout 2017, (AMZN -0.17%) looked as unbeatable as Mike Tyson during his heyday. The online retailer has grown despite the improved performance of some of its bigger rivals, and it made a smart move into brick-and-mortar by buying Whole Foods Market.

What happened

Through the first three quarters of its fiscal 2017, Amazon raised sales from $64 billion last year to over $72 billion in 2017. It also established its Alexa-powered devices as the prevailing standard for non-phone voice assistants and continued to grow its Amazon Web Services Business. In the Q3 earnings release, CEO Jeff Bezos ran down just a few of the company's accomplishments.

"In the last month alone, we've launched five new Alexa-enabled devices, introduced Alexa in India, announced integration with BMW, surpassed 25,000 skills, integrated Alexa with Sonos speakers, taught Alexa to distinguish between two voices, and more," he said.

An Amazon tractor trailer

Delivery has been a key advantage for Amazon. Image source:

So what

The improved efforts of its rivals, most notably Wal-Mart, meant that Amazon entered the year with some questions about whether it could keep up its torrid growth pace. Those questions were answered, and investors clearly liked what they saw.

After closing 2016 at $749.87, shares in the retailer climbed to $1,169.47 to finish 2017, a nearly 56% gain, according to data from S&P Global Market Intelligence. That's a huge jump for a mature company, but Amazon made it very clear last year that it was still at the beginning of a growth curve, not near the end.

Now what

Amazon has to fully integrate Whole Foods into its operations. That's not a major challenge, but it does require figuring out how to use those physical locations to increase its local same-day delivery.

In addition, Amazon must show that it can face intense competition in all areas of retail from competitors who are closing the delivery gap. On the hardware side, the company has to keep building out the Alexa/Echo ecosystem while seemingly every major technology company tries to move into that space.

Those are challenges, but nothing the company hasn't already shown it can handle. In fact, the biggest question facing Amazon in 2018 may well be whether it should buy another brick-and-mortar retail chain.