This is the best definition of the word I have found: deception is an illusion created intentionally to lead others down a wrong path in order to gain some advantage
The assumption in this definition is that deception is something we most actively do to others and not to ourselves. However, I think we can still apply it. One definition of the word "doubt" is "to be divided, or double-minded." In that, there is a reference to duplicity, of being divided inside oneself. It is possible to relate the two, to say that in order for a person to deceive himself, he must become divided in some way, doubtful.
Deception carries so many forms and is so common that we overlook it, we accept it. It goes beyond simple lying, and instead looks for the root cause for a lie. Why do we lie, to ourselves and to others?
I asked some friends of mine to give examples of deception in the world. Commercials, movies, politics, religion, feelings of competition or inadequacy among others, self-doubt. I mentioned the seeming manipulation of numbers for statistics that invaribly induce fear of the subjects they dissect: AIDS, ADD, bi-polar manic depression, pregnancy, the economy, the murder rate, etc.
Then there is that age old statement: if we were completely honest with one another, we would hate each other. That too is possible. But if you think about it, and telling the truth was the norm instead of the exception, we would soon develop a good and better way to tell the truth. Perhaps we would become instrisically more sensitive to others, more caring, less hateful. Since I do not know such a world, I can only assume it is not possible within our means.
The irony of truth is that those mediums supposedly dispensing truth often just replace your current deception with another, under the guise that this really is the truth. That, you could say, is competitive marketing for a target audience. Being fascinated with variety, fantasy, and boundless limitations in a finite world (read: planet; I will not speak for the stars), we are likely to believe what we see and when we cannot see, what we are told.
I won't present examples; you can do that on your own. I won't elude myself with solutions. But I do go back to one of several theories: whether we admit it or not, and if it is indeed possible to know the truth, we are strengthened by it more than we are weakened, depending on how we take the news. Being aware that I am being deceived is not winning the battle, but admitting that to myself places less emphasis on what I am told and more on what I believe to be true by experience, either my own or those of others. It's good sometimes to push the limits of the body or the mind, just to reinstate their elasticity, their abilities, but with the knowledge and acceptance that, just as our lives in these bodies are limited to finite time and circumstances, deception can also be limited.