Forum Discussion
Windows Update 2004 failures
Windows 10 will be tested internally with Windows team and then they release regular build to Windows Insiders who are users who contribute in testing Windows before release to everyone and when testing there was in acceptable level, then Windows will be released to more stable devices and slowly offer to other devices. In such method, it is less likely to face any failure or error and based on my experience such issues are very minor. However, consider large number of devices with different configurations such problem might happen.
Therefore, in case you face any problem, you may ask in Microsoft forums or/and send report through Feedback Hub app , so Windows team could investigate and they will work on improving experience for Windows users globally.
You mentioned about "large portion of the customer" which is wrong, there are too many successful installer and such failures compare to number of succeed installation is minor and Windows team working hard to resolve these issues and improving user experience.