What's the biggest mistake you've made as a founder?

Starting three different products before at least one matured

Hiring lawyers on a retainer before launching a product, lol. Sharing this here so no-one would do same stupid thing I did when I was starting.

Didn't build a audience before launch.

to get lost with all the possibilities we have ^^

Not starting any sooner.

Prioritisation. The initial goals for the startup should be to get the direction right in terms of product, market, possible users etc before throttling on execution and tech-related challenges. Going about the process without a hypothesis resulted in panic and random dart-throwing as a strategy.

Nothing new to this thread, but not jumping on marketing and sales earlier. If I were to go back, I'd start and/or hire marketers MUCH earlier.

My biggest mistake was to rely on not qualified engineer whole working on the first prototype of the guitar we're making. We had a problem just before showing it on the conference, as the prototype didn't work! We have managed to find a good engineer after this fail.

Be more resilient and focus on only one product

Biggest mistake was get a technical co-founder who had stopped coding in his career a long time ago. He may not be needed to code, but he is the final bastion if all code breaks down, (and it inevitably did)