It has been said many times that things are not always as they seem, and in the influence of the Moon this axiom is particularly true. In the moonlight, things that are benevolent during the day can suddenly seem dangerous and malicious. The very term "moonlight" is misleading because the Moon does not emit light of its own, it simply reflects the light of the Sun. Some people even claim to see the face of a man on the Moon's cratered surface, though of course such a thing is impossible and only an illusion. A lot of people who look for that face in the Moon know it could not be there, but they look nonetheless.
This card is one of the few Major Arcana with important animal symbolism, and with no human figures in the majority of cases. The Rider-Waite card shows a wolf and a dog; two members of the same genus, but the first is wild and the second has been domesticated. Both of them are shown howling at the Moon, however, and if a human were present in this scene he would probably be affected somehow too. Regardless of your place in the hierarchy of society or of evolution, you are still susceptible to illusions and deception. The Moon shines the same light down on everyone, though what you see when that light reaches your eyes depends on who you are, not on what you see.
In ancient religions the Moon deity was often a Goddess with ties to female fertility, because there was a visible correlation between the cycle of the Moon and the female menstrual cycle. While this association is still valid, the Moon of the Tarot tends to deal with fertility of imagination rather than fertility of body. The crayfish shown regularly on Moon cards is a sign of the emerging subconscious and its influence over the conscious mind, and for a mind closed to the messages of its subconscious, there can be a lot of illusion and deceptions to face. You can no longer tell what is real and what is just a manifestation of your fears and desires.
The ordeal of the Moon is the last challenge posed by the Major Arcana, in which you must travel in the dark, not knowing for sure if your path is the right one. There is no sunlight to guide you, no distant landmark in the hills to direct your steps, no one to travel alongside. This is a journey that must be made alone, in darkness and without a map or a compass. You must learn to rely on your own inner light to lead you along the true path. Any hesitation, any doubt, and that light will be extinguished forever. But if you believe, your light will shine forever, as brightly as the sun that will inevitably rise once this night has passed.
The Moon's appearance in a reading almost always means that something is not as it appears to be, and that vigilance and perception will be necessary to find that which is hidden before it is too late. In a generally good reading the Moon shows that not all is as wonderful as you would think. You may be idealizing the sitatuion, and ignoring the fact that potential for failure exists among success. A negative reading that includes the Moon often shows that you are letting your imagination run away with you, and that things are not nearly as bad as they seem. In both cases you must open your eyes and see what it really going on.
This card can also show times when you are not sure of your destination, or even of the path you are travelling - but you travel nonetheless. It's quite possible that you have lost your way, and are stumbling around in the dark. If you wait until the sun rises again the path may have changed and the opportunity could have been lost. So what should you do? The Moon is a card of intuition and psychic forces, so let go of your conscious mental blocks and let your intuition guide you. Not only will the way forward be revealed, but in a lot of cases you will learn lessons about yourself that will be valuable in later journeys.