Ask HN: What huge mistake did you make early in your career?

We’ve all been there — a seemingly huge mistake as an intern or Junior developer that you were sure would get you fired. What’s your story?

Mine: I nearly took down production by joining multiple large tables on non-indexed columns. Every time a product was updated on the site, MySQL would run my query and join across millions of records.

Infrastructure folks couldn’t figure out why the DB servers kept rubbing out of memory, and I very nervously made the fix. Thankfully the team was understanding (and appreciated that the person reviewing my code had messed up), but it was a terrible day.

Used the x.25 pad (telnet, for an older protocol family before internet became ubiquitous) command on the console of a vax 11/780. The pad break-back sequence to get back to the calling shell was ^P which was alas also the vax break to halt/debug command if you were on the main console. Took down the entire campus interactive logins

Didn't attend the hiring fair in my last year of uni, and missed the chance to become fully vested in Microsoft and like companies in the 1980s

I didn't listen to people who knew better.

Time and again I learned harsh lessons that shouted "Why didn't you listen? He/they/she said that would happen."

I worked for a company with an excellent mission but poor engineering growth opportunities for way too long.

I paid little to no attention to how my engineering efforts benefited the business.

I spent few years doing frontend while i hated it.