Having been in the same position I can empathize.

It's normal to be both excited and scared.

There are risks but also great rewards in creating a successful company.

Different people will have different ways of deciding when to go all in.

My approach (which may or may not be applicable) was to de-risk as much as possible, i.e. get as far as possible with the MVP before being all in.

Some important considerations were:

1. Having emotional/financial support from family/friends

2. Having completed all the go-to-market steps (even though the plan is never exactly how it turns out to be).

3. Getting comfortable with the financial implications e.g. investing my own money, not taking a salary in the first year, and the lost income.

4. Making sure it was the right time in my life to take such a risk.

Ultimately it could be a massive success or... not

If you fervently believe in your idea you will only find out if you try :)

Good luck!