Leaving a stable £100k job to build a nuclear startup, how did you handle the fear? I will not promote

Last year I started working on a hard-tech startup idea in nuclear engineering. About a month ago, it reached a stage where it felt presentable. At first, I wasn’t taking it too seriously, it started more as something fun to explore. But after sending a few emails around, a VC became interested. I initially mentioned a £10M raise, and they said they’d be open to looking at around £2.5M as a starting point. The idea revolves around two products aimed at de-risking a development. I’ve also started speaking wi