1. Too young

When you’re a little kid and you’re asked to do something hard, you can cry and say “I can’t do it” and the adults will probably let you off. As a kid there’s a magic button you can press by saying “I’m just a kid” that will get you out of most difficult situations. Whereas adults, by definition, are not allowed to flake. They still do, of course, but when they do they’re ruthlessly pruned.
The other way to tell an adult is by how they react to a challenge. Someone who’s not yet an adult will tend to respond to a challenge from an adult in a way that acknowledges their dominance. If an adult says “that’s a stupid idea,” a kid will either crawl away with his tail between his legs, or rebel. But rebelling presumes inferiority as much as submission. The adult response to “that’s a stupid idea,” is simply to look the other person in the eye and say “Really? Why do you think so?”

2. Too inexperienced

The best way to get experience if you’re 21 is to start a startup. So, paradoxically, if you’re too inexperienced to start a startup, what you should do is start one.
I’d advise people to go ahead and start startups right out of college. There’s no better time to take risks than when you’re young. Sure, you’ll probably fail. But even failure will get you to the ultimate goal faster than getting a job.

3. Not determined enough

How can you tell if you’re determined enough, when Larry and Sergey themselves were unsure at first about starting a company? I’m guessing here, but I’d say the test is whether you’re sufficiently driven to work on your own projects. Though they may have been unsure whether they wanted to start a company, it doesn’t seem as if Larry and Sergey were meek little research assistants, obediently doing their advisors’ bidding. They started projects of their own.

4. Not smart enough

You may need to be moderately smart to succeed as a startup founder. But if you’re worried about this, you’re probably mistaken. If you’re smart enough to worry that you might not be smart enough to start a startup, you probably are.
If you don’t think you’re smart enough to start a startup doing something technically difficult, just write enterprise software. Enterprise software companies aren’t technology companies, they’re sales companies, and sales depends mostly on effort.

5. Know nothing about business

You don’t need to know anything about business to start a startup. The initial focus should be the product. All you need to know in this phase is how to build things people want. If you succeed, you’ll have to think about how to make money from it. But this is so easy you can pick it up on the fly.

6. No cofounder

Not having a cofounder is a real problem. A startup is too much for one person to bear. And though we differ from other investors on a lot of questions, we all agree on this. All investors, without exception, are more likely to fund you with a cofounder than without.

7. No idea

Find something that’s missing in your own life, and supply that need—no matter how specific to you it seems.

8. No room for more startups

Nearly everyone who works is satisfying some kind of need. Breaking up companies into smaller units doesn’t make those needs go away. Existing needs would probably get satisfied more efficiently by a network of startups than by a few giant, hierarchical organizations, but I don’t think that would mean less opportunity, because satisfying current needs would lead to more.

9. Family to support

What you can do, if you have a family and want to start a startup, is start a consulting business you can then gradually turn into a product business. Empirically the chances of pulling that off seem very small. You’re never going to produce Google this way. But at least you’ll never be without an income.

10. Independently wealthy

I’ve come close to starting new startups a couple times, but I always pull back because I don’t want four years of my life to be consumed by random schleps. I know this business well enough to know you can’t do it half-heartedly. What makes a good startup founder so dangerous is his willingness to endure infinite schleps.
There is a bit of a problem with retirement, though. Like a lot of people, I like to work. And one of the many weird little problems you discover when you get rich is that a lot of the interesting people you’d like to work with are not rich. They need to work at something that pays the bills. Which means if you want to have them as colleagues, you have to work at something that pays the bills too, even though you don’t need to. I think this is what drives a lot of serial entrepreneurs, actually.

11. Not ready for commitment

If you start a startup that succeeds, it’s going to consume at least three or four years. (If it fails, you’ll be done a lot quicker.) So you shouldn’t do it if you’re not ready for commitments on that scale. Be aware, though, that if you get a regular job, you’ll probably end up working there for as long as a startup would take, and you’ll find you have much less spare time than you might expect.

12. Need for structure

In a good startup, you don’t get told what to do very much. There may be one person whose job title is CEO, but till the company has about twelve people no one should be telling anyone what to do. That’s too inefficient. Each person should just do what they need to without anyone telling them.

13. Fear of uncertainty

Well, if you’re troubled by uncertainty, I can solve that problem for you: if you start a startup, it will probably fail.
No one will blame you if the startup tanks, so long as you made a serious effort. I asked managers at big companies, and they all said they’d prefer to hire someone who’d tried to start a startup and failed over someone who’d spent the same time working at a big company.
Nor will investors hold it against you, as long as you didn’t fail out of laziness or incurable stupidity.

14. Don’t realize what you’re avoiding

Software companies don’t hire students for the summer as a source of cheap labor. They do it in the hope of recruiting them when they graduate. So while they’re happy if you produce, they don’t expect you to. That will change if you get a real job after you graduate. And since most of what big companies do is boring, you’re going to have to work on boring stuff. Easy, compared to college, but boring.
The thing that really sucks about having a regular job is the expectation that you’re supposed to be there at certain times. Even Google is afflicted with this. And what this means, as everyone who’s had a regular job can tell you, is that there are going to be times when you have absolutely no desire to work on anything, and you’re going to have to go to work anyway and sit in front of your screen and pretend to. To someone who likes work, as most good hackers do, this is torture.
In a startup, you skip all that. There’s no concept of office hours in most startups. Work and life just get mixed together. But the good thing about that is that no one minds if you have a life at work. In a startup you can do whatever you want most of the time. If you’re a founder, what you want to do most of the time is work. But you never have to pretend to.

15. Parents want you to be a doctor

A significant number of would-be startup founders are probably dissuaded from doing it by their parents. One is that parents tend to be more conservative for their kids than they would be for themselves.
The other reason parents may be mistaken is that, like generals, they’re always fighting the last war. If they want you to be a doctor, odds are it’s not just because they want you to help the sick, but also because it’s a prestigious and lucrative career.

16. A job is the default

This leads us to the last and probably most powerful reason people get regular jobs: it’s the default thing to do. Defaults are enormously powerful, precisely because they operate without any conscious choice.