So if worried, do this after a university degree; make sure not to let your skills rust; pick up practical experience... and then take a job (even temporarily) if things go downhill?

Broke is better than massively in debt - so don't take on debt.

Burnt out is more difficult, but at least somewhat in your hands (and pretty easy to come by in the course of a 'professional' career).

Unemployable? Now that one's wholly in your hands.

Being an entrepreneur seems like a fair, if still-unorthodox way of gaining a lot of life experience, fast. Surely this a lot healthier than many alternatives (including 'just keep your shoes clean and get a white-collar job', right en-route for potential mid-life crisis and regret?)

Surely, with the experience gained (learning to execute, if naught else), the whole endeavour is a success of sorts irrespective of what happens to the startup?