My standard advice to folks with corporate jobs who want to venture out on their own is this- hire a couple of guys to vet out your idea. Get the product market fit right, get the MVP done and have someone start talking to potential customers while you are still making a salary. If it is difficult to set aside $5K-$8K per month for this while you are working, it'll be significantly harder once you are not bringing in anything.
One of the biggest lessons for me when I did my own start up was that no one else is on the same timeline as you are. They go on their long holidays while you are refreshing gmail every minute to see whether they replied to your email.
All the while, you are trying to survive on whatever you have in your diminishing bank account.
Age also is a definite factor. If you are in your early twenties and used to surviving on $1500 of research assistantship from university, it is much easier to take random bets. You'll only learn from them. Once you are beyond a certain stage in your life, the equation totally changes.
I used to think this was bad advice (hiring out to others to vet your idea) and would actively advise startups against it, but the more I work with entrepreneurs the more I'm coming around to the view that this is a good route to take for someone who is working full-time and considering jumping off to do their startup.
By hiring out to vet the idea it reduces the confirmation bias that entrepreneurs face when researching their own ideas. As you noted, it forces an upfront financial commitment on the part of the entrepreneur, helping them realize what it will take to properly fund a startup at scale. It's also a time saver - trying to talk to potential customers (particularly for B2B startups) while holding down a full-time job is very difficult.
Of course, the entrepreneur should still be involved to the greatest extent possible, otherwise any early learning from the customer conversations, MVPs, etc. is lost...
