It's a common misconception amongst website owners. They believe that everyone is seeing what they're seeing, without regard to browser, browser version, device, etc. And while everyone would agree that it's important for a website to work and look good on as many devices and in as many browsers as possible, most people don't take the time to check their own website and assess how they're doing.
Do you only view your website at the office on an older, networked desktop machine? If so, take a few minutes and check it out at home on your tablet. Compare the experience and note any differences in available features? Is anything important getting lost?
Also, this may sound like a chore, but try loading your website while on vacation. It almost always yields new insight, whether it's from being in a different area of the country, utilizing a different connection speed, a new device, or simply a different mental headspace. It's easier to "see" the website as your clients and customers do.
Getting a new perspective on one of your top marketing tools can provide a valuable return on your time investment. And that´s good business whether you're a huge company or one just getting started. Try it soon!