This is an important realisation you have to have. Everything is, to some extent, flawed and everything you do is an attempt to reduce the level of imperfection. Everyone makes mistakes, things generally don’t go to plan so have to find ways of making sure that you find and correct issues before this is too late. Obviously, this is what review/testing and all the standard project stuff is about. But the crucial thing to remember is that it is the people who are flawed and collectively everyone and everything has to act to reduce problems.
The amount that flaws can be eliminated is simply another aspect of the Bermuda Triangle. If you have enough time and money, you can test/fix/control for many years and you’ll get close. This is a space industry thing, very expensive, one shot and it has to work as near to flawlessly as is possible. But even space stuff expects and gets some issues.
Most of us don’t work in that kind of industry and our scope for validation and verification is much less. There isn’t a problem with this. Its just a balance of risk. A website selling shoes can go live with issues. We won’t need a Shuttle mission to repair it.
The key point is, if you accept that things are inevitably flawed then you have to accept that it is your responsibility to organise the process by which collectively the project decides who to handle the flaws.
One obvious characteristic of an arse is that they tend to accept that corners are cut during a project (usually because they are too scared to declare a slip) but then blame people for there being issues at the end. Phrases such as “How did you let this happen?” can be heard. If you accept risk then accept the consequences of the risk not going your way. And, always accept that things are flawed.