If it ends up not being profitable, the bank takes back the house (or Twitter, or more likely the TSLA stock Elon put up as collateral)
If you can buy a valuable asset for $1 and have a bank cover $9 and it yields 10% return, you're making $1 from $1 invested (minus interest) compared to someone that bought it outright (making $1 on $10 or 10% return). The bank has no upside. If you invest in something bad though or the rate is too high the math changes and you lose 100% if the asset ends up being worth <= $9. That's leverage
On a related note, I always find the loans where the borrower takes on personal liability are in a completely separate category of risk. Anytime you put yourself in a situation where you could possibly ruin your future prospects or mortgage your future labor to a financial institution is much different than your net worth (and your investors' principal) simply going to zero.
In some states, such as California, a purchase loan is non-recourse, so you could walk away (and many did in the last housing downturn) and the bank can't do anything beyond take the house.
This means if you can weather the downturn you don't get wiped out, you borrowed 80% of the house to buy, put 20% down, it went down 30%, you were underwater, but continued to make payments, and now it's up 20% above where you started.
Margin loans against stocks, etc do not have this, so if you borrowed against $1k worth of stocks you had, and they dropped in value below what the bank wants you to keep as collateral, they can force you to sell at the lower price (or produce more cash/collateral). This means that with leverage you could be right in the long term but wiped out in the short term.