Since they depend largely on representation, a mere act of representation may suffice to excite a degree of the feeling hardly distinguishable from the actual one.

Thus, to imagine myself as contented is really to see myself at the moment as actually contented.

Again, the actor, though, as we shall see by-and-by, he does not feel all that the spectator is apt to attribute to him, tends, when vividly representing to himself a particular shade of feeling, to regard himself as actually feeling in this way.

Thus, it is said of Garrick, that when acting Richard III., he felt himself for the moment to be a villain.
We should expect from all this that in the act of introspection the mind is apt, within certain limits, to find what it is prepared to find.

And since there is in these acts often a distinct wish to detect some particular feeling, we can see how easy it must be for a man through bias and a wrong focussing of the attention to deceive himself up to a certain point with respect to the actual contents of his mind.
Let us examine one of these active illusions a little more fully.