Usually troubleshooting is applied to something that has suddenly stopped working, since its previously working state forms the expectations about its continued behavior. So the initial focus is often on recent changes to the system or to the environment in which it exists. (For example, a printer that "was working when it was plugged in over there"). However, there is a well known principle that correlation does not imply causality. (For example, the failure of a device shortly after it has been plugged into a different outlet doesn't necessarily mean that the events were related. The failure could have been a matter of coincidence.) Therefore, troubleshooting demands critical thinking rather than magical thinking.