In this system, you must accept nothing you are told, you must verify everything. Verification is the first principle of the Work.
This doesn't mean you should refuse to believe anything, and it doesn't mean you should simply accept things. It means you need to put the theories to the test, and find out if they are true.
This applies to all sides of your life, not just to these ideas.
For example,if someone tells you about the theory of human types, you should not simply believe it, and start to talk about it as though you know all about it: `Oh, I'm a Mercurial type', `He's a Martial'. You should not on the other hand say automatically `That's a load of rubbish, and not worth thinking about', at least, not if you want to learn something. What you need to do is try and put it to the test, in real life, not in a classroom, or in your head. You need to go out into the streets, in the midst of life, and look at people, and ask `Do these people fall into some kind of groups? Can I see the characteristics in them I was told I should be able to?' `What can I see?'
Verification is most important in regard to yourself. For example, you learn the theory that `man is asleep'. You need to observe yourself, and put it to the test---`Am I asleep?' It's no good to simply agree with someone `Yes, that sounds likely'. You have to see it. If you don't see it, you won't have enough force to really work on it. You need to see many times, over and over, many examples of your sleep, for it to penetrate your being, and for you to fully comprehend your situation. Also, sleep is different for each individual. You have your own mechanics. You have to verify what is true for you. It might be the case that what you are told is true for the person telling you, but not the case for yourself. You need to verify and observe to find out.
There are some parts of the system that can not easily be verified, for example, the theory that you are `food for the Moon'. For a cosmology theory like this, it may be best just to leave it alone for the time being. If it has no practical application for you, then it doesn't really make much difference whether it's true or not, and if you really have no way to verify about it, it might be better to spend time on things you can verify. Gurdjieff mentioned the theory of recurrence, about an idea similar to reincarnation. But he said very little about it, as really, it is of no practical use. This work must be practical and useful, and applicable right now, at this instant.
With verification the work never becomes boring theory, it never becomes old and stale, it is always continually being recreated in you. You can continually make more observations about human types for instance, and build on your personal verified theory.
If you don't verify, your work can not be effective, since you will only have a superficial understanding of it. When you verify something it becomes your own, something that can not be taken away from you.