Here is Paul Kirchner's interpretation of the themes of McMurtry:
1. Some people are competent, some can at least follow orders, some aren't much use at all and some positively need to be shot.
2. When you think you're on a mission you're usually just wandering around aimlessly.
3. Life may be by turns tedious, absurd, or cruel, but try to look at it as a learning experience.
4. Two ways to waste your life are looking for love where there is none and failing to recognize it when it is right in front of you.
5. Skill and determination count for something, but Fate wins every time.
I don't know about their applicability to McMurtry, but they seem pretty applicable to life to me.