Tesla (NASDAQ:TSLA) has beaten expectations at every turn, in the process becoming one of the country's largest car companies by market cap -- it's already surpassed Ford (NYSE:F) and is even closing in on General Motors (NYSE:GM).

But there's still a lot of uncertainty around Tesla, from its business model to its long-term plans to its giant Gigafactory. This level of uncertainty should rightfully make investors wary. That said, CEO Elon Musk has made a habit of beating expectations. 

Even if you believe wholeheartedly in Musk and in Tesla, though, one thing is pretty clear: There's no way 2018 will be Tesla's best year yet. But that doesn't mean it still won't be a good year for the company or its investors. Here's why.

A red Tesla Model 3

The Model 3 will be the key to Tesla's success -- or failure -- in 2018. Image source: Tesla.

The price of growth

It's easy for the stock of a young, scrappy company -- as Tesla was not too long ago -- to dazzle the market and crush expectations. And to grow very, very quickly.

Tesla had its IPO in 2010 with a per-share price of $17. By the end of that year, shares were trading at $26.63 a share, for a 56.6% gain. Shares didn't move much in 2011 or 2012, but all that changed in 2013, as Tesla's shares rocketed 344.1% to $150.43 a share. 

After that huge 2013 breakout, share-price appreciation slowed for the company. Annual share price appreciation for the company ranged between 47.9% in 2014 and negative-11% in 2016. Last year, shares were up 45.7% to $311.35 a share. 

That's still incredibly impressive growth -- Ford's shares rose only 3% in 2017, and even GM's were up only 17.7%. But for Tesla's shares to have their best year yet in 2018, they would have to rise to the ungodly level of $1,383 a share. And I can't think of any scenario -- not even if Musk brought a flying car to market -- that could boost the company's share price by that amount, given the size of the company and its financial situation.

The bull case

So even if Tesla's shares almost certainly aren't going to rise 300%-plus in 2018, what does the best-case scenario look like for the company?

Well, first and foremost, Tesla would have to fix the problems it's been having with production of its Model 3s. The company's latest -- and most affordable -- electric vehicle finally started rolling off the production line last June. But production has been plagued with delays. Although the company announced in early January that it had finally achieved a production run rate of 1,000 Model 3s per week, its original plan had been to achieve a run rate of 5,000 vehicles per week by the end of 2017. That goal has now been pushed back to the end of Q2 2018. 

If Tesla can meet its production targets, and make significant progress in delivering the more than half a million reserved Model 3s, it will do wonders not only for the company's cash flow but also for investor confidence in the company, which might push the stock price even higher.

Other ways the company could flourish include successfully lowering production costs and possibly introducing a new technological advancement or product, but the main thing that would make 2018 one of Tesla's best from an operational standpoint is to finally become a car company that can actually manage to successfully manufacture lots of cars. 

The bear case

There's no guarantee, though, that things will go Tesla's way in 2018. The company has already suffered something of a setback in the form of new tariffs on imported solar panels. According to the Solar Energy Industries Association, which represents solar installers such as Tesla's SolarCity, the tariffs will cause "unfortunate" near-term impacts for the industry. 

Of course, SolarCity represents a small fraction of Tesla's operations, but there's risk associated with the rest of the company as well. Tesla's debt has skyrocketed in recent years to nearly $10 billion, while its free cash flow is negative and getting more negative with each passing year. 

Then there's the question of valuation. With negative earnings, neither Tesla's P/E ratio nor its enterprise value-to-EBITDA ratio can be measured against its peers. But there's no doubt that its valuation has skyrocketed along with its stock price. 

The 2018 verdict

I'm cautiously optimistic that Tesla will get its act together and begin the long, slow march to profitability by improving production numbers and lowering costs. That said, it's far from a sure thing in 2018, and buying in now definitely isn't for the faint of heart.

However, if you believe in Musk's vision for the future -- and believe that Tesla can play a part in that vision -- 2018 might wind up being, if not Tesla's best year, then a pretty good one. But all that uncertainty means I can't in good faith recommend the stock.

John Bromels owns shares of Ford and Tesla. The Motley Fool owns shares of and recommends Ford and Tesla. The Motley Fool has a disclosure policy.