The Windows 95 UI designers wrote a paper going over their design methodology and how they incorporated feedback from real-world users at a variety of levels of computer proficiency into their design. https://dl.acm.org/doi/fullHtml/10.1145/238386.238611

For example, the reason for the single "Start" button in the taskbar was that they initially had multiple buttons for different specific purposes, and relied on a "Programs" folder on the desktop for launching programs, but found that this design didn't hold up in testing:

> Users had considerable difficulty deciding what each of the three buttons on the Tray was for and later had trouble remembering where to go for a particular command because their functions overlapped in certain contexts (e.g., to find something in Help, do you go to Find or to Help?).

> Users of every type were confused by the Programs folder. We thought that having a folder on the desktop with other folders and links to programs inside it would be a natural transition for Windows 3.1 users accustomed to Program Manager, while being relatively easy to learn for beginners. We were wrong! Beginners quickly got lost in all of the folders and other users had a lot of trouble deciding whether they were looking at the actual file system and its files or just links to actual files.

> The results from these studies and interviews greatly changed the design of the Windows 95 UI. In the early Windows 95 prototype, we had purposefully changed some things from Windows 3.1 (e.g., the desktop was now a real container) but not others (e.g., File Manager and Program Manager-like icons on desktop) because we were afraid of going too far with the design. We were aware that creating a product which was radically different from Windows 3.1 could confuse and disappoint millions of existing users, which would clearly be unacceptable.

> However, the data we collected with the Windows 95 prototype and with Windows 3.1 showed us that we couldn't continue down the current path. The results with beginning users on basic tasks were unacceptably poor and many intermediate users thought that Windows 95 was just different, not better.