Today in social media, I saw someone post something along the line of “why people say that index out-of-bound and dangling pointers are big problems? It is easy for me to fix.” We experienced programmers know how to use debuggers, and fixing those problem usually are not a big deal.
However, since these problems happen at runtime, they can easily go undetected during testing. If the bug happen on someone else’s machine or in a server, it is much harder for us to spin a debugger for it. The characteristic of undefined behavior also means that the problem may manifest somewhere far away from the bug, or the program will just silently run with wrong result.