Overview:
A thought is a complex, powerful, vivid thing, and a mind generates uncountable masses of them. All the churning of thoughts, the random recollections, that bubble to the surface of a mind are beyond imagination. Philosophers have reasoned that it is impossible for any finite intelligence to completely understand itself, for it would occupy the entire intelligence simply to contain itself without understanding, and at that point there would be no room for new knowledge. Most trained psionicists are inclined to agree with that assessment.
Thoughts, or "memes" in the language of psionics, seem to have a life of their own. The memes created by a mind generally remain within it and subordinate to it, but horror stories are told of psionicists who have created beyond their powers to control. Wherever they came from, rogue memes seem to wander the world, or whatever the equivalent of the world is for thoughts, and they are thought to be the primary cause of mental illnesses.
Minds have a complicated system of natural defenses, however. The masters can form more potent thoughts and have more precise control over them, but what makes psionics an art is that the minds they interact with, even those which lack even a rudimentary understanding of psionics, experience constant subconscious psionic activity. Moreover, when the subconscious defenses encounter an unusually strong threat (or perceived threat), this tends to manifest in the subject's mind as a feeling of acute uneasiness or anxiety.
Also, because psionics is such an immensely complicated thing, intentioned psionic activity tends to command the complete attention of its practitioners as they seek increased control over their own thoughts. This usually produces a starkly noticeable lack of focus on all other subjects.
Narrative:
I assure you, your mind is not being tampered with. You would probably know yourself, if it was, unless the tamperer were extremely skilled. Most people feel they are being watched, or suddenly become paranoid about nothing in particular. Your subconscious does try, in its own way, to alert you of danger.
You can be sure that I am not in your mind. In fact, you can be more certain that I am out of your mind than you can be of anyone else, because we are having a conversation. One of the distinguishing traits of psionics is that it tends to occupy its practitioners' full attention. You can perform psionic tasks without concentration--in fact, much of it is done subconsciously, especially if you are untrained--but the scale of psionics is simply so vast that one always feels that more attention is warranted to exercise more precise control. This is especially so when one is operating outside of one's own mind, and even more so when one is trying to be subtle about it, so as long as I continue to form coherent sentences, you can be reasonably confident that I am doing nothing.
Feeling safe now? No sudden surge of paranoia? Good. Now, let me see if I can tell you a little about psionics.
There are three common psionic disciplines which people practice: Kelite, Morian, and Shuez, named after the ones who pioneered them. Kelite focused on turning mental energy into effective strength as efficiently as possible, and the Kelite discipline is renowned for turning out the strongest memes. It is also infamous for the number of memes it fails to control, and most of the powerful escaped rogue memes one encounters are the results of failed Kelite experiments, so it is a somewhat dangerous study to undertake. Morian psionics are known for precision and discipline. Morian maneuvers tend to be effective at the greatest distance and are difficult to directly oppose. Shuez's discipline is concerned mostly with stealth and subtlety, and is the hardest to detect.
The curious thing about these organized disciplines is that they tend to mold your thought patterns with use, and do so in different ways. One of the results of this is that it is usually easy to tell a psionicist's area of expertise. Another is that it is very difficult to make extensive use of more than one of these disciplines at a time. They seem to have different ways of channeling and forming mental energy, such that the repeated use of one puts your thoughts in a poor order for using the other two.
Some even say that the use of the disciplines tends to weaken the natural, subconscious defenses of the mind. I wouldn't put too much stock in such rumors, though.
Hm? If you're feeling nervous, you don't have to stay. Sometimes its wisest to trust your intuition when around psionicists, especially if you don't have psionic training to rely on. Perhaps we shall speak more tomorrow.