How do you know whether to call it or to push through?

Every runner has off days, and these are part of the training process and part of life.  Some runners will continue on and finish an off workout or race even if it means walking and finishing grossly off any time goal, and others will cut it in order to have another chance at the workout or to recover faster to give another goal race a try.  I don't think there is a right or wrong approach, and many factors come into play when any of us make the decision.

Generally, I lean towards the first option:  finish no matter what.  In my 25 years of running, I have one DNF (did not finish) race to my name, in a half marathon that certainly should have been a DNS (did not start).  At the time I didn't know what was ailing me, but when I was finally diagnosed it was cryptosporidium, a parasite that causes intense stomach and intestinal distress (and that also left me unable to run much more than 3 miles at 9:30 pace for several days).  On the other hand, I once finished a marathon when I had walking pneumonia, and the feat of finishing entailed walking during the race (not my smartest life decision).

I've had workouts here and there over the years that I've called in, typically because of illness, pain, or knowing I was going to be so far off my time goals that the workout would do more harm (as far as wear and tear on my body) than good.  I've had workouts that felt off but that I pushed through and completed.  I had one of each in August, and it made me starting thinking about how I make the decision to call it a day, to push through, or to not start at all.

In hard workouts, if:

• I feel crappy and it's a key workout - push through; I may feel crappy on race day.
• I'm slightly off pace -  push through; they can't all be perfect!
• I'm grossly off pace - call it, especially if I can re-do it later in the week; at this point I don't think the training benefits I'm getting are worth the fatigue and wear and tear on my body (or the hit my confidence will take).  Calling it will allow me to recover faster and get back to training like I should be, plus if I am grossly off pace something else is most likely also going on (getting sick, sleep deprived, etc.).
• I feel like I'm getting heat illness - call it!  Once you have heat stroke it changes how your body deals with hot conditions for the rest of your life, and no one workout is worth that.
• Something hurts (suspected injury) - call it or DNS!  If it didn't loosen up and disappear on my warm-up, I'm not risking it.  Once lost workout is better than months of them.
• Confirmed injury - DNS, unless a medical professional has told me otherwise.
• I'm sick - DNS.  I run through about anything illness-wise, but I keep all of my running easy if I have anything worthy of calling an illness, so no workouts.

In races, if:

• I can continue without risking harm to myself, even if it means walking - push through.
• The only exception that might make me reconsider this is if I knew I was going to miss an important and realistic time goal, and would have another reasonable chance at it much sooner if I dropped, which would really only happen in a marathon.  Recovering from, for example, 14 miles is much faster than recovering from 26.2!  I can understand why elites drop marathons on off days.  I'm still not sure I'd do it, but it would enter my mind.
• I am risking my health - call it!  I would DNS a race if I were injured or sick beforehand, but if I suffered an injury or heat illness during an event I would not be ashamed to stop, because my long-term health and performance are more important than one day that would end in a crappy finishing time.  I mentioned above that I ran a marathon with walking pneumonia, but I was young and dumb, and would NEVER do that or anything close again.

There are plenty of unique situations I didn't cover here (e.g., if I were injured at mile 26.1 of a marathon, I would get in somehow!), and typically many factors are at play instead of one at a time, but this is generally how I would know.

How do you know whether to call it or to push through?  What scenarios did I forget to list?

The look of someone too tired to push through