What is a ‘good’ reason to miss an assignment or submit it late? What is a ‘bad’ reason? Who decides? How can your instructor know? My grading policies do not take a position one way or another about these questions: as an instructor, I cannot directly assess whether something was your ‘fault’ or not, only the outcome. Therefore, course assignments are designed to maximize flexibility in order to give everyone the benefit of the doubt.
If you miss an assignment or a class, in the vast majority of scenarios there is already a policy in place: please read the syllabus. Most essay deadlines have a “grace period” before which your grade will not be penalized for late submission. Many other grade categories automatically excuse the first several missing assignments or generously round upward from a percentage cutoff. Check the syllabus for specifics: 90% of the time there is no need to contact the instructor.
In return for flexible deadlines and other flexible assignment policies, I ask that you contact me only for personal matters so significant that they are not covered by the standard policies. Usually these situations are on scale of seriousness that we would need to involve advisors, doctors, or other university personnel to discuss a strategy for completing the coursework.
In short: for ordinary situations everyone faces over the course of the semester (getting a cold, skipping class for a once-in-a-lifetime concert, etc.) you are already covered and there is no need to contact the instructor. If something comes up that prevents you from completing coursework even beyond what the standard policies account for, we will consult with your advisors and come up with a plan.