If you're just starting your first company, it's likely that your biggest weakness in entrepreneurship is also your biggest strength as an employee.
As an employee, what makes you valuable to your employer is your skill as a functional expert, often in one (or at most two) narrow areas.
The in-house lawyer drafts and reviews contracts but can't sell (or feels it's beneath them).
The salesperson finds and closes individual prospects but has no idea how to market online at scale.
The engineer can write code but has no idea how to identify profitable market niches.
The common problem above is that most employees only really have strong familiarity (or competence) in their tiny role within the machinery of business - this means they have critical gaps in all the other skills needed to successfully run a company.
In other words, the biggest weakness of first-time founders who have just left their job is that they are often functional experts in just one (or two) area(s).
And this can kill your business - sometimes even before it really gets off the ground.
This only real exception is if you're coming from a senior (or senior-ish) role where you were responsible for high-leverage, big picture decision making that required you to regularly work cross-functionally with different business units.
If so, this would have allowed you to see, at a high level, how different key moving parts of a company work together in order to produce a viable, sustainable business.
But most of you aren't leaving senior level positions with broad decision-making responsibilities to start your company.
And since most of you fall into this latter category, you better find ways to get the skills you need.
Here are some ways if you're a brand-new founder:
Start a side-hustle, learn the ropes and get valuable market feedback with small-scale, low-cost experiments before quitting your job
Read books or watch Youtube videos that specifically focus on on-the-ground tactics (not just high-level strategy or vague notions of "management") of generating awareness in the market, and how to turn those into leads and sales. Recommendations include Jay Abraham, Dan Kennedy and Joe Sugarman
Take courses that have ideally force you to apply your knowledge with a capstone project so that you’re not just mindlessly consuming with zero application
Speak to a mentor on sites like GrowthMentor.com and ADPList.org to learn from someone who's ahead of you in areas where you are weak and to shed further light on “known knowns”, “known unknowns” and “unknown unknowns”
Out of the above list, I would put #1 and #2 as the most effective in helping you to fill any gaps in your skillset needed to run a viable business.
Consuming high ROI books and videos that teach you specific, on-the-ground tactical skills (such as copywriting and setting up sales funnels) will not only give you the immediate skills you need, but will also often unlock the “unknown unknowns” of bigger picture strategies (such as ways to use copywriting within the structure of your sales funnels in ways you may not have thought of before).
In many cases, these bigger picture strategies would not have been visible to you had you not gained certain on-the-ground skills in the first place.
Once you’ve done the above, take the skills you just learned and hone them in a real-world situation with your side business and learn from the ultimate teacher: the commercial marketplace.
My guess is that you'll find that having this safe learning period will ultimately be a lot more beneficial to your entrepreneurial success than quitting your job (and income) without key skills already in place.