May I ask whether you have much experience as a sole proprietor or solo founder?

As a solo founder of a startup that I've been running for almost the past four years, if I had anyone in my network that wasn't scared to death of leaving the comfort of a full-time job behind to join me as a cofounder, I would have brought them on board in a heartbeat.

One reason a technology startup is significantly more stressful than a standard business is that, by definition, you are in uncharted territory. Traditional businesses have loads of successful examples; the business model and value proposition to customers are both largely consistent. With most tech startups, you have to invent a new business model, create new technology fron scratch, and convince customers that your never-before-seen product or service is something they should spend their hard-earned money on.

1. The business model: Though there are a few general patterns available for web startups to use (e.g. freemium, ad-supported), every startup has to figure out how to become profitable within its particular niche. It's unlikely you'll find success by copying someone else's model exactly, while you can do exactly that in the small business world. Startups selling physical products (such as mine) likely don't even have freemium or advertising as options for experimentation, though there are some product startups exploring variations of those options.

2. The technology: Writing code and designing user interfaces is nothing like repairing cars. There's no doubt that there are a lot of intelligent, knowledgeable mechanics (even some who are also software developers), but there's a very large difference between understanding an existing system, and creating a new system from nothing but keystrokes. The common tasks of the mechanic can be done almost by instinct and memorization, leaving sufficient mental horsepower available for the few particularly tricky problems. Most startup-worthy software projects will involve intense creative effort at every step of development, which is far more mentally taxing.

3. Value proposition: Consumers already know they need a mechanic, or food, or a dentist. As a restaurateur, for example, you mostly need to convince willing consumers to come to your restaurant instead of your competition. A tech startup has to convince customers that they need to spend money on an entirely new category of product. Most people will agonize over the smallest expenditure if it's not part of their traditional purchase sphere (purchasphere?).

In summary, the stresses of running a tech startup, especially for someone in their 20s with at most a couple tens of thousands in savings, are far beyond what most solo founders can bear, and only those who are determined beyond reason (or already rich) should dream of going it alone.