If you're single, childless, and have a few thousand dollars in savings, quitting your job to focus on a side project or startup is very easy. You can achieve your dream in the next 24 hours. Here's the roadmap.
1. Give your employer your 2 weeks/1 month notice (depending on locale). Taking this step immediately is critical because the urgency and shock of the change will force you into being fast and practical about all the subsequent steps.
2. Create a monthly budget for yourself which assumes no income that you are not 100% sure about. So if you have interest from investments or a freelance contract that's a absolute guarantee you can include it. For most people the income side of this budget is going to be low or nothing. Your goal with this budget is to stretch your funds out for 6-12 months. The good news is that in 2017, the principle of geoarbitrage allows you to live on virtually any budget. If you live in the Bay Area your next step is going to be to move somewhere cheaper. On the cheapest end of the spectrum, I'll use Thailand as an example because I live here, you can get a basic apartment in the suburbs of Chiang Mai or Bangkok for $100-$500/mo, your initial arrival can be visa-free, and you'll live on delicious Thai food from a restaurant down the road for a few dollars a day. Network heavily with people in your intended destination before you even arrive because it'll make everything 100 times easier.
3. Now create a business plan for your new entity. The business plan should include a description of the product or service which you're going to market, how you're going to market it, what you're going to charge (start high), and any and all costs of development and operation including your own time. It should include monthly profit/loss projections (you're not allowed to use these projections in your budget, they are goals, not guarantees). The most important thing about your business isn't what product or service you initially offer. Once you have assets and control you can try anything you want. Until then the goal of your business is to make enough income that your assets are growing, no matter what that entails.
If you're leaving the country as a part of this process I would advise forming an LLC and opening a bank account before you go, as these things can be difficult from overseas. You'll be very busy trying to make money and living your dream so you don't want to have to deal with paperwork.
Prepare yourself mentally to work very hard for at least the next 6 months and do whatever you need to do to make enough cash. You will become practical and decisive, and you'll learn many realities about business, such as cash flow is king, very quickly. I got my start being nickel-and-dimed by agencies in India over Elance. It sucked and it was hard and it was 100% worth it.
There are many objections to this strategy which typically stem from risk aversion, or a desire to not worry about money. I would submit that if one objects to the risk, this plan is a personal growth opportunity: it will teach them how to handle stress, plan for contingencies, and so on. If the objection is that they don't want to worry about money, I would point out that money is just a way for people to quantify your value to them, and since no man is an island, there are great personal and financial rewards to be reaped from confronting this objection and discovering what other people truly value about you.
Doing step 1 first and now is the key. If your path brings you through Bangkok let me know and we'll grab a beer! I've seen many people succeed at this and a few fail. Your odds are better than you think.