When a company is growing, it's not the p&l that matters. It's the contribution margin (CM) (revenue less _all_ variable costs - including those "below the line

When a company is growing, it's not the p&l that matters. It's the contribution margin (CM) (revenue less _all_ variable costs - including those "below the line", like SG&A, that scale with your customer base) that matters. It can make financial sense to spend tons of cash (all you generate and then some through outside financing), as long as you're spending less to acquire and keep customers than they'll spend with you. It can be hard to tell, even for a good investor, if a company's true CM is positive, and my guess is that many fast growing companies have zero or negative CM. I'd guess that Airbnb's is quite positive.