Did people who had money in FTX lose it?

I'm sorry to hear about the recent collapse of FTX. As a professional practitioner in the field of cryptocurrency and finance, I'm sure you're aware of the significant impact this event has had on the crypto market. I was wondering, did those who had invested their money in FTX lose everything? Was there any way to prevent this from happening? And what are the lessons we can learn from this incident to ensure the safety of our investments in the future?