Do you know what your strengths are?
Do you know what you're weak at?
If you can be honest with yourself about your strengths and weaknesses, then you can start to act on them.
You don't necessarily need to improve where you're weak – just admitting that you're weak in a specific area can help you to decide if you should get better there, or find another solution.
For example, if you're running a business and you're weak on financial knowledge – you can choose to improve there, or you can choose to give that role to someone else. The only option you can't pick is to continue to be weak in that role and hope something changes by luck or magic.
The only caveat to improving all your weaknesses is you end up in the age-old situation of being a jack of all trades and a master of none. In the early days of any business, this is not necessarily a problem. But as soon as you have a team – of even, say, five people – it's time to start thinking about what you want to be a master of.
Do you know what your strengths and weaknesses are? If not, don't be afraid to ask those around you. People are often very nice, so it's likely they won't be forthcoming with your weaknesses. So make it easier for them – if there's an area you feel isn't your strength, simple ask those around you "Others have told me I could improve in X area – would you agree?"
Once you're clear on your own strengths and weaknesses, and you know where you want to improve, then it becomes a lot easier to worry less about your weaknesses and shortcomings.