The question you really want to ask is: what's the expected risk/reward ratio? And if you're in any kind of demand for your professional skills, your risk is your opportunity cost (which you can reasonably well predict), plus the small chance of some horrible disaster that leaves you unable to finish (which you can't predict, but applies mostly independently of the amount of career risk you're taking). Then there's the the thing that people get hung up on: the risk that the project will tank, and you'll have an inexplicable gap on your resume. If you're in a place like the valley, this risk is largely imaginary -- as long as you comport yourself professionally, taking a chance on a startup isn't going to hurt your career.
Initially, assume your expected reward is near zero. You're walking on to the casino floor, and you're there to have a good time. You want to keep the game going as long as you can, but you're not prepared to gamble more than you can afford to lose, and you assume that the house has the odds. Your calculation is: how much am I willing to lose on this activity?
Later, if you achieve some success, you can modify your risk/reward calculation. Is your project growing? Bump the expected reward. Did you raise money, and can now afford to pay yourself? Reduce the risk. Decide where your personal loss threshold is for this particular bet, and when you cross that line, stop.
In my opinion, the thing you should worry about is not financial risk, but life risk: is this what you really want to do with your one-and-only youth? It's a much harder question to answer, but a good place to start is: do you really, honestly, truly give a shit about the thing you're planning to build? If not, stop now. No amount of "success" will make it worth the pain you're going to endure. So if what you really want is comfort and a peaceful life, get a job somewhere, and don't regret your decision. Otherwise, proceed forward with the knowledge that you're doing something you have to do, even if only for a little while.
* your start-up is acquihireable - you have a lean highly talented team with no visa issues concentrated in one geographic location
* you produce IP that will retain value after startup fails - patents, trade secrets, know-how, maybe stuff you can open source and put on your resume when the time comes to send one out
* the business you're working on can theoretically survive on customer revenue alone without a cash infusion from an investor
Stage 0: a bunch of friends have drinks one night and dream about starting a startup. 99% will not even go further
Stage 1: one or more co-founders actually meet regularly and try to make progress on starting their startup - still about 99% will not succeed
Further stages: get an office, or quit and work full-time on the idea, or raise a small seed, etc... Still close to 99% failure rate.
I seperated from the military to work on a bootstrapped project that started with myself and expanded to include a few others, my relocation to LA, etc. It eventually failed. Statistically, it's just another failing number. To me it was a very enlightening and educational experience and I don't think my partners at the time and I would be where we are now without that experience. Best of luck to you!
I certainly do agree with finding the right strategy for you "Keep your head about you when others are losing their heads and blaming it on you." I decided to build while I have full time job. The builds, releases and pivots are slow but I am managing my time well and I am certainly not starving.
It is also true that the majority of restaurants fail. But the time to study that statistic is when you are deciding when and where to start you restaurant and what kind of food/service to provide. It is not after you have already hired the staff and sent out flyers about the grand opening.
But it's not zero percent. In your case that's as good as 100 percent!
Then the percentage won't matter.
(But yes, to answer your question, it is pretty close to 100%).