I think the most frequent illusions in my own life are in my own head as a result of the vagaries of communication between people. For example, for a thought/statement to pass from someone else’s head into mine (or vice versa), it must first be converted into words (and body language, inflection, etc.) and those signals must then in turn be received interpreted my own brain. This complex transaction provides multiple possible junctures for the intended message to be misconstrued and misunderstood, as the words used to relay it are highly imperfect.
Once I receive a message, my brain has to make a judgement call on the intended meaning – was the other person intending to insult me? to compliment me? Usually my interpretation is colored by my own insecurities and fears as well as areas of overconfidence.
Ultimately, these misinterpreted statements can cause me to convince myself that what are perhaps very untrue things about myself (or others) are true and vice versa. I think we also have a tendency to believe that “everyone” thinks a certain way about us if we perceive one of our own insecurities/fears to be validated by just one other person.
I think this form of illusion happens every day and is particularly dangerous: when people believe things that are untrue about themselves and have radically different perspectives of the world (and people) around them, we create personal insecurities and ideological enemies. I would also imagine that a great number of mental illnesses deal with these illusory negative perceptions of oneself (and of the world’s attitude towards us).