One principle of the Toyota Manufacturing process is Genchi Genbutsu - "go and see for yourself". It's the idea that to truly understand a problem and find the best solution, you must encounter things first hand and not from a distance. Consider the following example of Toyota chief engineer Yuji Yokoya:
Yokoya had many epiphanies. In Santa Fe, N.M., narrow downtown streets convinced him that the new Sienna should have a tighter turning radius. On the gravel of the Alaska Highway, he understood the need for all-wheel-drive. After squinting in the Mississippi sun along the Gulf Coast, he ordered roll-up sunshades for the second- and third-row side windows. ... Soon after its debut, the 2004 Sienna became the car critics' darling. Through the first 11 months of last year, Sienna sales were up 60 percent over the same stretch in 2003 - Smartest Company Of The Year
Think about how this principle might be applied to UX design. The things we build should serve a purpose. Often the purpose is centered around an end user who is trying to achieve certain tasks, but the end user is not doing these things in a hip downtown office space in the middle of the workday. No, they're using your website in a totally different environment than the one it was conceived and created in. Do you have a holistic understanding of how people use your product?
To gain a more meaningful understanding your user and their needs - to make the best product - you must experience what they experience.
If you're building a restaurant website go to the restaurant and ask patrons about their dining experience from beginning to end.
If you're building an inventory system, perform inventory tasks to find patterns and ways to speed-up the process.
If you're building a product dashboard, use the product yourself.
The easiest way to uncover the true purpose and function of your product is to go and see for yourself.