A few years and much avoirdupois ago, I was a fairly good long distance runner. I had run a dozen marathons, a few 25Ks and assorted ten-milers, all at around a 7-minute pace.
In the course of most races there were times, of course, where I began to falter, where my pace would begin to flag. In time, I learned how to handle my fatigue. I would drop my wrists to waist level, stand up straight and count my steps to a thousand.
I would push myself to do a thousand paces strong. Then when I had finished those thousand steps, I would refresh my count and do a thousand more. This approach was particularly helpful when facing a long, steep uphill. A hill can be daunting but counting to a thousand is mechanical--something to occupy the mind when the body isn't cooperating.
I find counting to a thousand is useful in the long slog of advertising, too.
There are strenuous uphill miles in every project we face--weeks and weeks of pain before the finish line can even be sniffed.
It's best to drop your arms, stand up straight, count and work through the pain.