The advice "just start writing" is technically correct but completely useless without the part nobody says out loud
Everyone tells you to just start writing when you're stuck. What they don't tell you is that the first thing you write almost certainly won't be the actual start of the essay — it's just the thing you need to write to warm up enough to find the real start.
Most of my best opening paragraphs were written last. I'd write the whole essay, figure out what I was actually arguing, and then go back and write an intro that matched the essay I'd actually produced rather than the one I thought I was going to write.
The "just start" advice works. It just works differently than people describe it — you're not starting the essay, you're starting the process that eventually produces the essay. Those are different things and treating them as the same is why people get discouraged when the first thing they write isn't very good.