You are the creator of the universe. You created this universe last (that is, this most recent) Thursday at noon, and it will expire next (that is, this upcoming) Thursday at noon. Everything you perceive as predating last Thursday was planted by You in order to create the impression of an ancient universe governed by natural laws. This planted evidence includes all of your memories and all physical evidence of prior events.You created the universe as a test for you. Everyone who is not you is an aspect of You, placed here to complete the environment for the test. Everyone but you is aware of this.
The purpose of this one-week test You created for yourself is to discover the limits of your own judgment and character.
You expect of yourself ethical behavior, including treating others well, given the illusion of the reality of this universe. Part of this universe is the illusion of the existence of others. You are expected to treat others as you would wish to be treated.
You also expect yourself not to perform left-handedly. You may have feelings or urges of left-handedness, but these are shameful and sinful feelings, and it is wrong to act upon them. This is not to say you are precluded from using your left hand at all, only from favoring it. For instance, it is acceptable to You to hold the pot with your left hand while you stir with your right, but it is not acceptable to write with your left hand.
A key part of exercising sound judgment is being skeptical. You expect this skepticism to include disbelief in such things as God or gods, telekinesis, homeopathy, astrology, faith healing, and ghosts. Human belief in these things was created by You as a temptation for you.
You are not expected to believe in Last Thursdayism, since belief would require faith. In fact, believing in it would cause you to at least partially fail the judgment part of the test You set out for yourself. You are expected to treat Last Thursdayism as a religion: no more, no less.
If you succeed at this test of ethics and judgment, you will be back to Your former Self, with the attendant power to create universes. If you fail, you will be tortured in proportion to your failure. This torture will be infinitely worse than anything you can imagine or that is described in planted memories or works in this universe.
See the catechism.