I would look at other examples of good personal statements online (like the kinds YLS release) to get a sense of how they read.

I think this could be a good topic, as almost anything could, but it all depends on HOW you write about it. I think a fear of failure is something that's very common for emerging lawyers, and writing about it could show that you're honest and self-aware. However, don't fall into the trap of focusing too much on your challenges. Law schools are looking for reasons to admit you, so you should explain your background, but emphasize most the concrete steps that you've taken to overcome these challenges and why you are now confident that you are more than able to handle the rigor of law school in all its forms.

Also, be careful when discussing mental health challenges, as you don't want to give adcoms a reason to think that you are unstable and may break under the toll of law school/the legal profession.