Starting a business is easy. You can start a business in a few hours.

Starting a profitable business is a lot harder -- even if you put all of your time (and a lot of your money) into it. The all-in approach is also a lot riskier, since the more time and money you invest, the greater your risk. So how can you live out your entrepreneurial dreams while minimizing your risks and maximizing your chances of success?

Simple: Start your business. And keep your full-time job. Except in rare cases, keeping a full-time job is the best approach for first-time business owners. That's true whether you intend your business to "only" be a side hustle, or whether you hope to someday quit your full-time job.

Of course, it's also the hardest approach: Sacrifice, discipline, and a massive amount of hard work are required.

But that's OK. If you aren't willing to work hard and sacrifice, your new business will fail whether you keep your full-time job or not.

Here's how to keep your full-time job and make your startup a success: 

Cut every personal expense to the bone.

Almost every business venture requires spending money before making money. Even if money isn't required, time certainly is -- and time is money. Some small businesses take years to turn a profit.

A huge percentage of startups fail because they run out of money. Even if they don't, chronic money problems can lead to poor long-term decisions.

Never assume personal savings will see you through. Eliminate every bit of personal spending that isn't necessary.

Before you start your business, cut your personal expenses to the bone.

Be indispensable at your full-time job.

When small-business capital and cash flow are tight, losing your full-time income is the last thing you can afford. Make sure you're indispensable. Work as hard and efficiently as possible. Get more done than anyone else, so you can leave on time without regret -- and without raising concerns about your performance and dedication.

Working incredibly hard at your job will make your evening and weekend time yours, not your full-time employer's.

Set a formidable daily schedule.

When your "normal" workday ends, your startup workday begins. Decide how many hours you think you can spend on your startup every evening.

Then add 25 to 50 percent to that number.

And then commit to your schedule. Write it down, and if your schedule says you will work from 5.30 p.m. to 9 p.m. every evening, and from 8 a.m. to 3 p.m. on weekends, work those hours.

See the schedule you create for your startup the same way you see your schedule for your current job -- as nonnegotiable.

Then put your head down and do the work.

See your formidable daily schedule as an opportunity, not a burden.

Say you start a consulting business. Once you land a few clients, you'll be working every evening and most weekends. That's not a bad thing.

That's a good thing. Landing clients means you generate revenue.

You may have to get up early every day to take care of emails and voicemails before you head off to work. In large part, your clients will choose your work hours for you.

Don't complain, even to yourself. Having demanding clients is great because it means you actually have clients.

Resist the temptation to feel sorry for yourself. Happily pay the price -- it's a price most other people won't pay.

Reinvest all of your profit.

At first, you'll be tempted to spend some of the profit you make. That's natural. We all want to be rewarded for our work.

But don't do it. Reinvest every dollar you earn. Use your profits to set up the business infrastructure you need (not the one you want, but the one you need). Buy supplies. Buy the equipment you've had to rent. Increase your advertising budget.

If nothing else, save some cash to tide you through the inevitable revenue downswings.

Don't think of the profits from your startup as income. Think of those funds as a tool that will further establish your business.

Keep your full-time job longer than you want.

Deciding when to quit your job and go into business full-time is the hardest decision you will make.

It's impossible to make an objective decision when you're tired, stressed, sick of your full-time job, sick of your boss, or when you just want your life back.

But don't quit too soon. When in doubt, hold out.

Always focus on numbers, not emotions. Let the numbers indicate when it's finally time to quit your full-time job.

Don't worry: You'll know.