Actually this is not a matter of smartness and paying attention. Real world projects expanding over years and decades behave like complex systems and it can be

Actually this is not a matter of smartness and paying attention. Real world projects expanding over years and decades behave like complex systems and it can be guaranteed that they will have correctness issues. Furthermore there's always a tension between speed and safety in C and C++ programs which make them particularly prone to these errors. In fact there are probably many people who are competent enough to write safe C++ code (C's a lot harder), but they code in environments where this is unlikely to happen.