Exploring the opposite: what do unfragile startups look like? I worked for one but the catch is it taking much longer, like decades, to grow to a unicorn, as it is run more like a business. Generally the growth is from reinvesting revenue not outside investors.

Yes exactly — a lean, bootstrapped startup is a much "safer" bet, but also has much more limited upside potential. There are still a few unicorns out there that took that path, or switched to being VC backed later in the game!