It's a good time to own stock in Tesla (TSLA), as the company's shares passed $500 for the first time, giving it a total market value of more than $90 billion. For comparison, that's more than the combined market value of Ford and General Motors. Of course, the main difference between Tesla and other large tech companies is that they regularly make money.

In fact, Tesla's recent surge is largely due to its surprising announcement back in October that it had made a profit, along with the fact that it delivered more than 367,000 vehicles in 2019. That number represents a 50 percent increase over the previous year. The fact that making a profit was a surprise tells you everything you need to know about Tesla right now: It's incredibly good at making cars--not so good at making money. 

Look, I mean that sincerely. Tesla's cars are really, really good. And the Model 3 is the best-selling electric car by a long shot. But until recently Tesla has had a much harder time actually making money. That's not a knock on the company, necessarily. 

In fact, Musk was pretty clear that his goal with Tesla was "to help expedite the move from a mine-and-burn hydrocarbon economy toward a solar electric economy, which I believe to be the primary, but not exclusive, sustainable solution." He even called it his "secret master plan," never mind that it was posted on the company's public website.

And the company has certainly proved that electric cars can match internal combustion engines in terms of range, features, and performance. In fact, Teslas have actually managed to beat them in several cases, especially in performance.

Still, the fact that the stock has doubled since October shows that investors are relieved that the company has started to make money. That wasn't always a given.

But it's not necessarily a good thing. Look, I'm not a stock guy, but there is a simple reality about these things. Expectations can be finicky, and right now, despite the fact that Tesla is beating expectations, Elon Musk has a reputation for, well, overpromising. Remember when he promised he'd take the company private when it hit $420 per share?

He usually manages to deliver some version of those promises, but the expectations on Tesla are now higher than ever. Oppenheimer raised its forecast for Tesla's shares to $618, which is staggering for a company that generates $24 billion in revenue and has only been profitable a few quarters. Creating huge expectations is great for generating hype, but is hype always a good thing?

Sure, if you can deliver. 

Correction: An earlier version of this column incorrectly calculated the value of Tesla. It's worth around $90 billion, not $900 billion. The article also made a comparison of the value of Tesla to that of several large tech companies; that comparison has also been removed.