Odd ... why put your own money at risk when you have access to unlimited blank checks? Some kind of weird personal asset defense play?
1. To diversify their finances. Going all in means every bet, if it fails, could be your last. (Less applicable for someone with Elon's name recognition.)
2. Some ideas don't scale down. Building a big rocket is a different game from building a small one. The lessons from the latter will apply roughly, at best, to the former. Same with tunnels.
3. To get intellectual and political buy-in. When people invest in something, they take ownership--financially and emotionally. Having shareholders who you can deputies to fight your battles can sometimes beat a hired hand.
Loans are the simplest to understand -- it's leverage. If you think you can double your money in a few years with a business plan, and that opportunity scales passably well to more money than you have in your bank account, you can take out a loan. To use your language, leverage is just "betting on yourself" even harder.
Taking on investors is different in that you can't ruin yourself doing it, but similar in that it increases your resources in a way that you hope will more than pay off over time against the cost.
Musk probably doesn't feel like he needs that validation, so the main reasons to take outside money would be leverage and diversification. The downside is some loss of control.
Boring under LA to relieve congestion creates a MASSIVE opportunity that, when refined, can be deployed into other markets and eventually used in space. It's a genius move.
Musk is a definite bad ass.
The nature of shorting is that you make money only when stock drops significantly in a short period of time.
If stock is flat, you loose your money. All of it.
If stock drops less than premium you paid for the option, you loose money.
If stock drops a day after your option expiration date, you loose money.
This year there were a couple of dips (~20% in short period of time) where you could have made money shorting. Caveat: if you timed it perfectly and good luck with that.
To put real numbers: a 3 month short will cost you about 10% of stock price. To make money stock price would have to drop more than 10% and you would have to execute the short at the right time in that 3 month window (as opposed to waiting for even bigger drop and loosing because the stock went up).
Even with TSLA stock gyrations in the last year, that's a bet very unlikely to have been profitable for most people.
Edit: you’re also more likely to have lost money buying Tesla over the past year vs shorting it, so it really hasn’t been “expensive” to short it.