Snowmageddon, Snowpocalypse, Sneaux Day.
Call that stretch we endured at the end of January what you like. My friends who live in areas of the continent which have all that winter stuff were in a state of "schadenfreude;" the German term for "bless your heart," and not in the good way, either.
I should have seen it coming, weeks ago.
First, my loving bride informed me she's slated to work an IT conference in Miami Beach. Then comes a text message from one of my athletes; an illness has laid him low. The next morning's long run was a very solitary affair.
The week's catch-phrase was going to be "Semper Gumby." Those of you who speak U.S. Marine probably have that term down. For the rest of us, that's "always flexible."
One of Timothy Noakes' 14 Laws of Training recommends to not set a training schedule in stone. A modicum of flexibility or modification can mean the difference between happiness and frustration. There are days when your run training should be set aside completely, and others where a minor modification to duration, activity or intensity may be all that's necessary.
When it comes to a running-related injury the immediate knee-jerk response is to say "no running, period." Exercise which closely replicates running form and with sufficient intensity without aggravating the injury is best. The next best choice is exercise which replicates running, at lower intensity and without aggravation. Third-best is exercise which is intense and doesn't aggravate what hurts...kind of like the joke where the guy goes to the doctor and says, 'Doc, it hurts when I do this...'
If it hurts, don't do it. Heal up and figure out what caused the injury in the first place.
Most runners are obsessive-compulsive, and will try to train through every illness, from the lowest level creeping crud all the way to two steps shy of the Black Death.
Are you having a problem breathing? The "chin rule" is probably the best counsel for airway issues; if the airway or breathing problem comes from inflamed sinuses, sniffles and such you might be all right with an easy run. If the congestion source is below the chin level you'd be best off taking at least a day away, and pay close attention to how you feel on a daily basis. If you're sick and tend to use gym facilities, it's best to stay at home. Don't pass what icky-doo which got a hold of you on to someone else. And if you work out in a group, for heaven's sake, use universal precautions...that means no sharing of anything.
Some days you simply feel like a "semi-solid waste-to-receiver sack capacity mismatch" exists, favoring the former. Fatigue, pure and simple, may require a variation or temporary cessation in activity, duration, intensity, time of day...one, some or all of the above factors.
It might be a day where you simply need to curl up on the couch in your sweats and read a good book. Unless you're a parent of a really young person, in which case all bets are off.
The family is support structure number one for every runner. You might be a participant in this sport for a few years or a few decades, but you got to live with most of these folks for a long time. Right off the bat, I have fervently agreed that "parentism" tops all other belief structures and constraints, especially when the children are not able to fend completely for themselves.
Infants, toddlers, and rugrats with issues? No arguments from me on those fronts. If you can slide the workout time "to the left/right" or adjust the duration so as to maintain domestic tranquility, by all means consider what must be done.
Youth, teens, young adults; it better be a genuine emergency, defined as near-life-threatening. Otherwise the issue falls in the category where it can most likely be worked through or around.
There are social functions which come rarely within a lifetime, and where family attendance and participation is strongly encouraged. If the immediate family understands your passion for running or fitness they might, say, remind others in the family about the habit of "the crazy runners," and to adjust accordingly...or at least leave you a seat on the aisle.
For very few persons is the 60-minute run part of a typical day in the office. There are employers who are really understanding when it comes to the physical fitness needs/wants/aspirations of their workforce. Others are encouraged to let workers adjust their schedules and take time off for exercise, given certain constraints. And if you're fortunate you'll know in advance whether there's a major project on the horizon. Or a business trip. In those cases you might have to adjust the schedule, make certain there's a workout facility in the hotel, or a good path, or a running club or track. This category is often the easiest to plan around.
In closing, the choice to run is not a strict zero-sum "you do or you don't" equation. A little of some exercise is better than a lot of no exercise.