I've spoken before about building talent, and expressed my belief that there is no such thing as natural talent. You are good at what you do because you put the work, the time, the practice into your passion. I do believe that people may have natural inclinations towards wanting to learn certain skills, but that's the only thing beyond your control that has anything to do with your skills.
Now, it's pretty much guaranteed that you will have weaknesses in your skill set. Nobody can be good at everything. The question you face is at what point is it worth learning a new skill? If the skill is directly related to the product or service you're selling to others than the answer is always "right stinkin' now!" It starts getting into grey areas with skills outside your field, but still directly relate to your business in some form.
In this hypothetic scenario you are a freelance illustrator, and you need a website. In the modern world we all need websites to even register as a legitimate business to the vast majority of people. However web development may not be something you're good at, after all you've put your effort into becoming a better illustrator. Is it worth it to learn web development and build your own website from scratch? If it's something that you want to learn then go for it, but that approach is not ideal for everybody.
Your best bet is to outsource. That doesn't necessarily mean hiring somebody who has the skill set, although that's an option if you have the budget. There are products out there that make it easier to build your web presence. There are pre-built content management systems like Kirby and Wordpress, and complete solutions like Squarespace. There are also software tools like Flux and Adobe Dreamweaver. All these options have their own learning curve, especially if you want to make the most of the tools, but they make websites far less intimidating.
I personally outsource a lot my business to other tools. I use Squarespace to build and host my website because I am not very good with web development, in fact it stresses me out. I use Stripe for all my payment processing because I don't have to worry about building my own system, dealing with credit card companies, and also because I value the security of my clients information which I'd rather put in the hands of someone who does this for a business.
Outsourcing your weaknesses can end up costing you money. Squarespace costs me more than a regular hosting plan, Stripe takes a larger cut of my income than the credit card companies would. But the question you have to weigh is wether it's better to put in the time to learn this stuff, or give up a little extra money. Maybe it's better to focus on your core business and the skill set that your customers come to you for. Maybe you want more control and putting the time into a new skill is the only way to achieve that.
What I'm saying is evaluate your strengths and weaknesses. If it's not worth it to you to learn something entirely new then it's not worth it. But if you can put in the time to learn something new and make it awesome then it will be immensely valuable.