You cannot evaluate an insane belief system from within it

T-9.VII.6. You cannot evaluate an insane belief system from within it. 2 Its range precludes this. 3 You can only go beyond it, look back from a point where sanity exists and see the contrast. 4 Only by this contrast can insanity be judged as insane. 5 With the grandeur of God in you, you have chosen to be little and to lament your littleness. 6 Within the system that dictated this choice the lament is inevitable. 7 Your littleness is taken for granted there and you do not ask, "Who granted it?" 8 The question is meaningless within the ego's thought system, because it would open the whole thought system to question.

T-9.VII.7. I have said that the ego does not know what a real question is. p176 2 Lack of knowledge of any kind is always associated with unwillingness to know, and this produces a total lack of knowledge simply because knowledge is total. 3 Not to question your littleness therefore is to deny all knowledge, and keep the ego's whole thought system intact. 4 You cannot retain part of a thought system, because it can be questioned only at its foundation. 5 And this must be questioned from beyond it, because within it its foundation does stand. 6 The Holy Spirit judges against the reality of the ego's thought system merely because He knows its foundation is not true. 7 Therefore, nothing that arises from it means anything. 8 He judges every belief you hold in terms of where it comes from. 9 If it comes from God, He knows it to be true. 10 If it does not, He knows that it is meaningless.

T-12.IV.2 The search the ego undertakes is therefore bound to be defeated. 2 And since it also teaches that it is your identification, its guidance leads you to a journey which must end in perceived self-defeat. 3 For the ego cannot love, and in its frantic search for love it is seeking what it is afraid to find. 4 The search is inevitable because the ego is part of your mind, and because of its source the ego is not wholly split off, or it could not be believed at all. 5 For it is your mind that believes in it and gives existence to it. 6 Yet it is also your mind that has the power to deny the ego's existence, and you will surely do so when you realize exactly what the journey is on which the ego sets you.

T-12.IV.3. It is surely obvious that no one wants to find what would utterly defeat him. p223 2 Being unable to love, the ego would be totally inadequate in love's presence, for it could not respond at all. 3 Then, you would have to abandon the ego's guidance, for it would be quite apparent that it had not taught you the response you need. 4 The ego will therefore distort love, and teach you that love really calls forth the responses the ego can teach. 5 Follow its teaching, then, and you will search for love, but will not recognize it.

- ACIM (about the ego’s insane belief system)