What all can/will go wrong on launch day?

Hi everyone, As I’m preparing for our upcoming launch I’ve read through numerous posts on everything you should do to prepare for the launch. In a recent thread @austinarmstrong commented about being ready for things to go wrong. I read this and wanted to hear more on it. Anything like not thoroughly testing onboarding and users being unable to sign up, or more product hunt related things like waiting too long to announce your launch. What are some examples of unexpected or unfortunate scenarios you’ve encountered and how did you adapt? Share your personal experience so those prepping to launch can be aware :) We’re launching https://www.producthunt.com/prod... in a week and are working on getting all of our ducks in a row for that