I noticed that there are several possibly *negative* components of running:  

Being hot / sweaty / thirsty. 

In cardio-vascular terms, breathing hard or having elevated heart rate. 

Feeling tiredness / soreness in the legs or pain in legs any part of the body. 

Being bored / unmotivated. "I'd rather be doing something else." 

The first two don't bother me (unless I were running outside in high heat).  

Usually, my legs will feel tired before my cardiovascular system.  I am not really tired in any meaningful sense. After the run, or next days, legs will feel sore, but a *good sore.* I don't mind sweating, because that is the body's system for cooling down. 

So the key is mental, receiving the signals from the body and processing them in the way I want to. It is a training of the mind. Now, since the weak part, as far as the body is concerned, are the legs, then I don't have to worry as much about other components. The weakest part of the mind is the part that wants to quit at a certain point, but then I can just slog through those parts. Presumably the muscles in the legs will get used to running and not protest as much.  

***

Back windshield shattered yesterday. Extreme cold temperature, and then heating up the back window with built-in heating coils to melt the ice, must have stressed the glass too much. The dog got sprayed by skunk; then I noticed she had peed in the bed at some point during the day. [I don't even own a dog!] 

Bad things happen in threes.