The startup road is littered with bodies of dead startups and crushed dreams. The chances of your startup making it and ever being successful are extremely low. Many of those dead bodies were perfectly capable of success, but uncontrollable changes in the markets or life in general can strike a final blow, with no warning, at any time.
Being the CEO of a startup is much like being Leonitis when he commanded his 300 Spartans to face the thousands of Persians in the narrow passage with the almost certainty of death. While this is exciting to think about, the consequences of defeat are real. Yes, it might not cost your life if your startup fails (though, sadly it could), but there is so much at stake. The physical toll and stress from the startup will definitely take years off your life.