What would make you quit a job within the first six months?

If the work didn't matter to anyone.

I've experienced meaninglessness in work. I worked at Dunkin' Donuts in college. The product was objectively bad for the people buying it. My hands were in the closed loop. People hurting each other in the most ordinary, polite way. And I learned something there that's shaped every career decision since: work you don't believe in is just your body in a building while your soul sits in the parking lot waiting for you to finish.

I wouldn't quit over hard work. I wouldn't quit over a steep learning curve. I wouldn't quit because the code base is messy or the process is imperfect. I'd quit if I looked at what I was building and could not identify a single human being whose life was better because it existed. If the product was pure extraction. If the users were the product. If the business model depended on making something slightly worse to capture slightly more revenue.

I'd also quit if I had zero autonomy. I don't mean I need to make every decision. I mean I need to be trusted with some decisions. If every line of code requires approval, every architecture choice is dictated, and my job is to translate someone else's spec into syntax, that's not engineering. That's transcription. And I'm not a transcriber.