"We often judge of a thing according as we have it at heart; for we easily lose true judgment through private affection.
If God were always the one aim of our desire, we should not so easily be disturbed at resistance to our opinions.
But there is often something lying hid within, or occurring from without, which draws us also along with it.
Many secretly seek themselves in what they do, and know it not.
They seem also to continue in good peace; when aught is done according to their will and judgment; but if it be done otherwise than they wish, they are soon moved and become sad."
Thomas A Kempis.
I like this quote, and the way I take it is, that our way of thinking, "have it at heart", and our emotional reaction to things, "private affection", are the things lying hidden within and are the filter we interpret circumstances with and then allow to draw us along into narrow or self centered thinking.