Every day, you do a hundred jobs, some of which are occasionally handled by specialists. You make a sales call or give a presentation or answer the phone, you design a slide or create a simple spreadsheet. While you are busy being a jack of all trades, you're competing against professionals. The recipient of your work doesn't care that you are also capable of doing other things.
Some define a professional as a person who does industry standard work for money. A professional speaker, for example, could give a presentation on anything, not just the topic on which you're passionate about. When you compete with professionals, you have a problem, because generally speaking, they're better at what they do than you are.
But there are ways to think your way out of this situation. Hire a professional or be as good as a professional. Realize that professional quality work is not required or available and merely come close. Or do work that a professional wouldn't dare do, and use this as an advantage.
The first option requires time and money you might not have, that's probably why we don't do it in the first place.
The second is a smart option, be as good as a professional, particularly if you do the work often and the quality matters. Graphic design and marketing are two examples that come to mind. The first step to getting good is admitting that you aren't. Invest the time and become a pro if it's important.
The third option is worth investigation, but it's what you've probably already decided without putting words to it. Is the assumption really true? Does your customer/client/employee actually believe that they haven't been shortchanged by your amateur performance? Think of all the sub-pro experiences you've had as a customer, instances where someone was pretending to be a chef or a bartender or a computer geek but just came up short. Not a good way to impress anyone.
The fourth option is really exciting. The humility, freshness and transparency that comes with an honest performance might actually be better than what a professional could do. If you're the only person on earth who could have done what you just did, then you're a fabulous amateur. You can't skate by when you refuse to mimic a professional. You must connect in a personal, lasting way that matters. That's difficult, but the professionals have no chance to compete with you. Sometimes only you can cover all the bases because you're the only one that knows where the bases are. Being an amateur on purpose, not because you have to, can lead to learning many skills to a professional level.