Living in a State of Delusion

What happens when you lie to yourself so repeatedly that you actually start to believe it? What exactly switches in someone's brain to take them from complete clarity to delusion? Is it an involuntary defense mechanism that's triggered when someone can't take the strain of responsibility? Or is it completely voluntary - a learned skill to save one from hating themselves?

I have told lies, but who hasn't? They're usually small, the sort of lies you tell as to not hurt someone's feelings. You wouldn't tell someone you loved they looked hideous even if they did. That is unless maybe you were going out and you didn't want them to be embarrassed or something. Just white lies like those fill everyone's day. It doesn't make you a pathological liar. So what does? Would believing your own lies make you a diagnosed pathological liar or would that just make you mentally unwell?

There have been times I've lied or made excuses for myself about various things in life more than once. On top of that, a few of those times, I've told myself and others the same lie so many times that I don't remember what the truth was in the first place. If that wasn't sick enough, it made me feel so much better believing that I had, in fact, done no wrong (when in the definite reality I had). So do other people do this or should I be concerned?

Would this make me a good liar or would this make me gullible? Could I be both at the same time? I feel like a walking contradiction; one big, fat, living, breathing oxymoron. Given, I haven't lied to that extent all this year. Last year might have been another story but, when it comes to last year, my mind has been diligently working away, sorting what to keep and what to toss out like yesterday's news. However, the lies I've told in the past, the ones I've accepted as true, remain in a dream-like state whenever they cross my mind. By living the truth and then forcing myself to believe a lie it almost seems as if the whole event was fabricated; as if I might have dreamt it or experienced it in another life.

I feel as though my thoughts are odd and unorthodox, like there aren't many people out there who would formulate these types of inquiries on their own. They might be interested and begin to ponder after someone ignites their thought process for them (i.e. reading my own questions), but I don't know if they'd ask these questions all on their own. I feel as though my philosophical side is quite a bit outside of the perimeter of the metaphorical "box". Then again, I often feel like I ask too many questions all together.

I'll be asking questions like these all my life. I can't seem to turn that part of my brain off, so I suppose it's destined to remain on until nature and the aging process turn it off for me.