Travis-CI had some staffers connect to the wrong database and truncate production tables. Needless to say this caused an outage and disrupted their business. Hopefully they didn't lose too many customers, but they certainly did not help their reputation. I'm sure there are more than a few customers trying to decide if they continue to trust the company or move their Continuous Integration (CI) processes to another platform.
I've done this before. Not shut down a company, but I have actually truncated a production table by mistake. Well, not TRUNCATE, I mean, who runs that. But I have run a DELETE without a WHERE clause and killed a lookup table in a production database. Fortunately I had a copy of the table elsewhere and could rebuild it in minutes. Only a few customers had their work interrupted and only for a portion of our system. The point is that I've been a very good DBA, with a lot of success and experience, and I still make mistakes.
Often this type of mistakes comes about because we get busy, and we keep connections open to different systems. When we might be developing code against a schema that is close to production, it's easy to forget which database we're working on. Someone calls with a problem or we fight a fire, and we run some code. We fix the issue, stress bleeds away and we go back to work, but forget to switch connections or tabs. Then we run some code that would be fine in development, but causes issues in production.
SSMS has colors for a connection. SQL Prompt has tab coloring by system and database, as do some other products., which can help, but it isn't perfect. One thing I've found with colors is that if I use them constantly, my mind starts to filter out the color. I don't always realize the outline of the tab is a different color. This is especially true if I have the need to switch back and forth between both production and non-production systems. I've tried running two instances of SSMS, which helps, but at times I'll forget which one I'm working with and make a connection to a production server from a non-production instance of SSMS.
Ultimately, we need to be careful. I know one friend that has no access to production and must hop through an RDP session and connect to a production database. However, if you run your RDP session in full screen, how often would you forget that you're in the SSMS on the hop system and not in SSMS on your local machine.
I don't know if there's a good solution. Many of the convenience features that make life easier, like reconnecting tabs when I restart SSMS are great, however, they can compromise security and safety. I don't know if there is a good solution, but I'd certainly like more checks against ad hoc issues occurring in production systems. Maybe some sort of lock against certain instances that prevents destructive execution on certain instances or databases without some confirmation. I love SQL Prompt preventing me from running code without WHERE clauses, but that isn't always enough. At least not for me.