Before you quit your job for an idea
Every week someone resigns for an idea they have never shown to a paying stranger. A few of them are right. Most needed one more season of groundwork.
Test it while employed
Evenings and weekends are enough to find out whether an idea works, and they are the cheapest laboratory there is. Build the smallest version that lets a real person get the benefit: one service delivered by hand, one page taking bookings, one spreadsheet doing the work the app would do later. Keep the job until strangers, not friends, have paid more than once. Employment is not a cage here. It is the funding round that asks nothing back.
Money rules that keep you honest
Know your monthly number, the boring sum of rent, food and everything else, before you resign. Keep six months of it aside, in a separate account you do not see daily. Never fund advertising with borrowed money at this stage, because ads bought with fear teach you nothing about the idea. A runway you can see buys calm decisions, and calm decisions are the whole game.
The honest signal
Compliments are free and therefore worthless as evidence. The signals that count cost the other person something: money, a signed letter, a booked slot they show up for, a second order without prompting. Collect those instead of applause, write down each one with the date, and resign the day the list stops scaring you.