When should one startup ?

If you’re building a product, get a Product Market Fit by pitching to a closed audience or building a prototype for a closed audience or getting some investment. If you want to offer services, I’d say you need a strong network and experience handling 5-6 clients. In either cases, have a runway of 1 year is unmarried, 2 if married and 3 if married + kids. ymmv. And a Plan B, if it fails. Unless your idea is exceptionally good (a rarity) or you’re entering a market that has very few providers but multiple potential takers, I wouldn’t recommend quitting and building.

Started small, went full time when it grew. Key is to start small and not think too big from day 1. Get your first 100-1k customers, then you'll know if you have something that'll grow or not.

Take care of liabilities and ensure you have runway of 2-2.5 years. I am assuming initially you intend to bootstrap before deciding if funding makes sense or not for your business. Frankly there is little downside and a ton of upside in starting up as long as you have solid skills. The worst that can happen is opportunity cost of 2 yr of starting up. However as long as you are hardworking, smart, scrappy and tenacious - you will learn at an insane pace. You will be able to grow much faster in your career even if the startup fails. Building startups is like a game. You need to play enough iterations and ensure you don't die - incur insane debt/ break down mentally or financially or relationship wise. Eventually you will get better, enjoy the game and hopefully win the game.