This question was asked over at Quora. Some great insights and answers there, but just posting this one by Greg Tapper:
I've started 5 companies-- several (fortunately) very successful...and a couple painful failures. I've learned far, far more from the failures than the successes.
There's one rule and one rule only to business success: NEVER drop the ball. The "ball" is everything related to the business. A growing business screams like a baby. It never stops asking for your attention. Take your eye off the ball for 1 minute and you'll slip off the treadmill.
Businesses fail because people lose their focus. Look at every successful company, and it all gets back to that. They lost their direction and focus. Success is virtually guaranteed when you're absolutely obsessed and absorbed in the business.
1) Never outsource anything important. Ever. There's no such thing as a brain transplant. You can get a new heart, a new arm-- mechanical things-- but you can't replace the central nervous system.
2) Never trust anyone with anything critical. No one. You have to be the one to take care of it. And don't even trust yourself. Constantly question how you're doing, what you're doing, why you're doing it.
3) Never stop thinking about what can go wrong, because something is always going wrong.
4) Never trust your reports who tell you everything is fine. Nothing is ever fine. Things are always breaking. Things are always going wrong. (We say: "rejoice, things are breaking. We're growing!"). Breaking isn't necessarily a bad thing. Frustrating yes, but not bad. It usually means you're growing.
5) Treat your customers better than your spouse. Take your customers for granted, pay the price. Without customers, your company is a high school science project.
6) Businesses are 100% about cash flow. Cash is king. Never forget that cash is king. Did I mention that cash is king. Guard it jealously until you have an embarrassment of riches. Then let your investors complain that you're not paying a big enough dividend; and then you can ease off the gas. The truth is, nobody cares about your big idea and your cool technology. Not investors, not employees, not your spouse, and not your mother. What they care about is: are you making a lot of money or not? Or, if not, are you clearly on the path to creating such tremendous, protected asset value that one day very soon the business will start kicking off tons of cash. Then your investors and your spouse and your employees and your mother and Inc. Magazine will all shower you with praise and lift you up on their shoulders and go marching out of the room and singing a song about you. Google isn't valuable because it has great technology-- it's because those mofos mint money. And FB is just sitting on a goldmine of active users, so they are highly valuable. But it's about money, and nothing more. (Btw, money is a *measure*, not a goal.)
7) You fail because you let things fail. And at the end of the day you'll blame every person you've ever met for your failure. You'll give 100 reasons why it's their fault. How that employee didn't do his job. How that customer screwed you. How that investor didn't invest when it was really important. How the damn developers just sat on their asses and delivered dog crap to you. Then you'll wake up one night when it's just you sitting there alone, and you'll realize that you're the entrepreneur and you're the only one holding the bag of responsibility. That company is yours, even if you're a 1% equity holder. Employees are as loyal as cats. Investors have lots of other deals going on. Customers always have other options, and they're pretty good about reminding you of that. So at the end of the day, it's just you. You and your company. Because, you see, the company is you. You are the company. You are singular zen being. That's when the lightbulb goes on and you have to be a big boy or big girl and say: "I take absolute and total responsibility for the success or failure of this company. It will succeed in part by me, and I will get partial credit for its success. But it will fail in full by me, and I will take 100% of the responsibility for its failure." Sorry, you only get partial credit, but 100% responsibility.
A metaphor: When I taught rock climbing as an undergraduate at Berkeley, we did big climbs in Yosemite. And it was common wisdom that the people who fall are the ones who let themselves fall. The ones who climb to the top are the ones who persevere every minute and insist their way to the top. They never even let their toe budge an inch. Their fingers cling to the rock, often in pain, invariably bleeding. But they hold on and insist their way to the summit.