I have to imagine the failure rate of pushing a product that people don't need would be high, and the ability to support a product that they do need would not be compatible with the side-project concept. Am I wrong in thinking this?
However, if you build software for doctors that avoids the regulatory compliance problems, then get it expanded out to 14 hospitals, then raise, then have staff, you can then go back and do that HIPAA compliant SAAS solution that you initially wanted to. Which pretty much describes my path over the last 3 years
If you were able to dodge that, then, salute!
EDIT: And, I will admit, there has been an amount of conflation of the term 'side-project', and 'startup' and 'mvp' and 'project' and 'product' over the (esp. last two) years that confuses me from time to time. I often lose the thread on context. My apologies if my comments reflect my lack of appropriate modern contextual understanding.
I think it's quite possible to have both. Have a full time job, work on a side project, and if it becomes successful enough to quit your full time job, then do so. Startup without the uncertainty!
Granted, now you've pushed the odds of your startup failing from 95% to perhaps 98% (since you're not devoting all of your time to it), but what do a few percentage points matter at that level anyway? Replacing a 5% chance of winning the lottery with a 2% chance doesn't mean you should no longer play (especially since you've eliminated the stress of potentially starving).