If you had around $27,500 of Tesla (NASDAQ:TSLA) stock a decade ago, today you’ve have $1m. And because of the depreciation of the pound over the period, you could have reached millionaire status in sterling with around £24,000 (because Tesla shares are denominated in dollars).

It’s a great example of how picking the right stocks can be incredibly rewarding.

However, I don’t believe it’s going to get easier to pick these long-term winners. One reason for that is private equity. SpaceX, OpenAI, and Anthropic — three companies with a market-cap greater than the entirety of the FTSE 100 — have sought funding exclusively from private sources, until now.

In other words, retail investors might not get the opportunity to invest in high-potential companies like SpaceX until they’re already sizeable entities. SpaceX, it’s rumoured, will IPO with a valuation around $1.5trn. That’s the same as Tesla’s worth today.

The biggest company in the world?

Cathie Wood, the outspoken CEO of ARK Invest, maintains one of the most audacious price targets on Wall Street. She predicts Tesla will reach $2,600 a share by 2029 — that’s more than six times its current price of around $420, valuing the company at over $9trn. This would make Tesla the largest company in the world, based on today’s valuations. Her bull case envisions shares hitting $3,100. Even her bear case sits at $2,000.

The foundation of Wood’s forecast rests almost entirely on robotaxis, not electric vehicles. ARK’s analysis suggests nearly 90% of Tesla’s enterprise value and earnings will come from its robotaxi business by 2029 with gross margins potentially soaring from the current 16% to as high as 90%.

The problem? Tesla’s current stock price sits far below even the bearish scenarios ARK projected in previous years, and the robotaxi rollout remains limited.

Grounding those forecasts

I absolutely believe Tesla could be among the most valuable companies in the world in next decade. Robotaxi’s could be everywhere — I’m not sure I agree with Wood’s timelines — and the Optimus robot could be widely utilised from factories to homes.

However, the big ‘if’ is the technology. The forecasts assume Tesla dominance, but that’s not a given. Lots of companies are trying to follow Tesla into the autonomous driving and robotics era, so it may only secure a piece of the pie.

That said, I don’t dispute Tesla’s ahead of the game. I often use the ‘level 4’ self-driving on my Tesla, and it’s largely very good.

This is where investing becomes particularly risky. If Tesla stock was cheap — trading around 15 times forward earnings instead of the current 202 times — then it would probably be quite an easy risk/reward calculation.

But unfortunately, Tesla’s a phenomenally expensive stock and the potential’s very hard to quantify. That’s why it isn’t a stock I’ve added to my portfolio. It’s very tempting but this just isn’t my style of investing.

Having said that, investors may want to consider it if it meets their risk profile. It could be worth $15trn in 10 years, but equally it could be worth a lot less than it is today if it fails to deliver.

So yes, it could make someone a millionaire if they had enough invested.