Why does all bundles and upgrade have issues?

 Hi all, this problem has been bugging me all the time when I'm performing upgrades on existing PSFT application especially HCM. When i perform the patching using CA there is sure problems popping up such as Cannot insert duplicate key row in object 'dbo' , Unable to insert NULL value and etc. If this happen on a HCM which has customization then i still can accept. But it also happen on a freshly installed HCM. With no customisation just purely standard settings. Imagine if a HR bundles have like 50 scripts to run and almost half of it having issue with different tables, this slow down the patching process all together.