Here's a story about the road not taken and how expensive it can be. Tesla Inc. (TSLA) CEO Elon Musk just couldn't resist weighing in on Microsoft Corp. (MSFT) co-founder Bill Gates' wealth trajectory, and honestly, the numbers are wild enough to merit attention.

The Trillion-Dollar "What If"

Investor Michael Arouet posted on X this week about the current top 10 richest people in the world. The list is notable for who's missing: Bill Gates no longer makes the cut. Even more striking? Former Microsoft CEO Steve Ballmer sits at number eight with a net worth of $166 billion.

This represents quite a fall for someone who held the title of world's wealthiest person for 18 of the 24 years between 1995 and 2017, according to Forbes.

Arouet's post focused on a fascinating counterfactual: Gates decided to sell his Microsoft position based on advice from legendary investor Warren Buffett, CEO of Berkshire Hathaway Inc. (BRK-A) (BRK-B). Buffett encouraged him to diversify his holdings, which seemed like sensible wealth management at the time.

If Gates had ignored that advice and held onto all his shares, Arouet calculates he would now be "the world's first trillionaire, worth twice as much as Elon."

With Microsoft's market capitalization now sitting at $3.6 trillion, Gates' net worth would theoretically be around $1.5 trillion if he'd retained his full stake and hadn't embarked on his massive philanthropic initiatives with ex-wife Melinda Gates.

To be fair, Buffett's advice wasn't unreasonable. Microsoft shares spent years going sideways after the dot-com crash, taking roughly 15 years just to recover to their previous highs. Few could have predicted the company's extraordinary surge over the past decade.

The $10 Billion Tesla Short

Musk couldn't resist jumping into the conversation, bringing up his favorite topic when it comes to Gates: the alleged short position against Tesla.

According to Musk, "Bill Gates placed a massive short bet against Tesla" roughly eight years ago, representing about 1% of the company's total outstanding shares. Musk claims this position has cost Gates approximately $10 billion as Tesla shares have climbed substantially over recent years.

It's worth noting this isn't the first time Musk has publicly discussed Gates' supposed short position. The two billionaires have had a frosty relationship, with Musk previously suggesting Gates' short bet undermined his credibility on climate issues.

On Wednesday, Tesla shares dropped 4.62% to close at $467.26, while Microsoft was essentially flat, down just 0.05% to $476.12.

The broader story here is about different approaches to wealth. Gates chose diversification and philanthropy. Ballmer held his Microsoft shares and rode the wave. And according to Musk, Gates bet against the future of electric vehicles. Each decision comes with trade-offs, though some trade-offs turn out to be worth hundreds of billions of dollars.