In a long chain of managers the manager above will only hear "there was an issue and it's fixed". The upper manager doesn't really have the time and the will to dig into the details.
Whether you're talking about a new Twitter or Reddit, which used to go down all the time (like, constantly), or some business startup, a downtime of 30 mins or so no-one really cares about, in my experience. At worst you'll get a phone call or two, a few emails, but if you handle them compassionately you'll be fine.
You can run a startup serving thousands or tens of thousands of customers on a single server, with no micro services, a simple server-side MVC setup and never have a $600 a year dedicated server even break 15% CPU.
I once took down a server by flooding the email server with error emails, which generated more error emails, which ran out of disk space, etc., etc. Took an hour to get the site up again.
Barely a blip in revenue. Client finally coughed up for proper email hosting rather than running their own server on the same box as their site, as I'd been advising them for 4 years.
This is a gross over-generalization. There are many kinds of problems in computing that can be approached by a startup AND which require large amounts of compute. The soup du jour is machine learning problems.
As for downtime, OP has a perfectly valid point. If you're building a B2B application, the customer has already taken a risk on you. If you go down in the middle of a busy workday, even for 30 minutes, you can be damned sure that someone at your client is getting some heat for taking that risk rather than going with $BIG_CO.
The early adopters are going to give you slack.
As for the tiny number of startups solving ML business problems, compared to the thousands of web apps launched daily on product hunt, if your USP is computing power and special tech, then obviously this advice does not apply.
Edit: You should really disclose you work on AWS when discussing this sort of stuff
Yikes. Is this irrelevant attempt to disarm them why we have these obnoxious "disclaimers" all over HN?
It's an absolutely meaningless gesture.
You're imagining the inconsequential downtime of Twitter or Reddit instead of a small B2B company trying to hook its first customers.
As the CTO of a small startup 0.1% downtime translates into vast quantities of lost trust and irreversible damage to our brand. Netflix goes offline for a bit they have some angry customers, and maybe lose some cash, but they'll still be chugging along. However, if we're down for a while our customers, who are already taking a risk trusting a new company, may disappear forever, and as a smaller/newer company the overall brand damage is far worse.
While I largely agree with the premise that companies over do it on infrastructure. I strongly disagree that my up time is less important than that of FAANG companies.