Believing versus Delusion

Hi! I struggle with believing sometimes because then I have the thought that I must be delusional. Then, for example, I watched the documentary on Elizabeth Holmes on HBO. If you haven’t seen it, “The Inventor, Out for Blood in Silicon Valley” it’s riveting.
I think she truly believed in her idea and she kept taking actions despite there being a lot of evidence that she was in fact not producing what she said she was. I think to this day, even after being prosecuted that she still believes. On one hand, is there any other way to be? So I get that, but on the other, she produced a result that doesn’t reflect her belief. SO, either she didn’t really believe, or she’s just straight up crazy? I only use this extreme example, because although I never want to stop believing in myself, at what point do you read the signs and shift directions?