I've worked for other companies that have this problem. I've seen it come crashing down before.
Every week the CEO gets up in front of the company for the all-hands meetings and is just so bubbly enthusiastic about how fast they're growing, and isn't this great, and thanks to everyone for all the hard work, and go team, and isn't the amazing growth just INCREDIBLE, and yay for us, etc. The problem is once the obligatory cheers die down, EVERYONE HAS TOO MUCH TO DO. The rah-rah atmosphere is a two-edged sword. It makes so that people feel they aren't being a team player if they stop and say "Wait a second, we're growing so fast we aren't doing very many things really well, and at this pace, it won't be long before we aren't doing ANYTHING well." Meanwhile, employees are getting silently burned out, pressured to feel that this is such an oh-so-very-special place to be lucky enough to be that a few jugs of midnight oil burned for the cause is nothing we should be complaining about.
Twilio is something of a cult, and people are expected to work very long hours and often in a slapdash fashion "for the cause".
The company has an unusually niche technology stack, so most people coming to work here have a steep learning curve and have to acquire a larger-then-average amount of proprietary knowledge. Which means the people who have already climbed that learning curve are not easily replaced.
