DESIGN FLAW - Not at all,
If your user inputs a value that locks up the code, or it suffers from heat stroke, or maybe once in two years, the power supply can't meet the demand of exceptional circumstances (two fans, and a servo while running in reverse on a Thursday !!). Maybe a power spike loses all your retained data.
If we could predict it, the issue would have been tested and corrected before shipping !
Depending on the product, any of these may require a return, or support visit at a minimum $20-30 per hour plus parts and travel/shipping.
No replacement unit, or design flaw, just an unexpected operational problem that could destroy your reliability.
For example, I have over 100 units located more than 50 km from anything like support or a person to press reset.... Without a watchdog, or remote capabilities, if anything had gone significantly wrong... someone would need to drive out there with parts, diagnose - or simply restart the device. Maybe replace the unit. (One was kicked by cows, another had a relay failure, yet another was hit directly by lightning - not product failures thank goodness !, but all of them were more than 200km away from me.)