When is fear not good?

Hebrews 10:31
It is a fearful thing to fall into the hands of the living God.
Fear is terrifying if we have to fall into the hands of God without having made peace with him.

Genesis 26:7
And the men of the place asked him of his wife; and he said, She is my sister: for he feared to say, She is my wife; lest, said he, the men of the place should kill me for Rebekah; because she was fair to look upon.

Joshua 17:16
And the children of Joseph said, The hill is not enough for us: and all the Canaanites that dwell in the land of the valley have chariots of iron, both they who are of Beth–shean and her towns, and they who are of the valley of Jezreel.
Fear is not good if it keeps us from doing the things we ought to do. We are not meant to live in fear.

Numbers 13:28-31
Nevertheless the people be strong that dwell in the land, and the cities are walled, and very great: and moreover we saw the children of Anak there. [29] The Amalekites dwell in the land of the south: and the Hittites, and the Jebusites, and the Amorites, dwell in the mountains: and the Canaanites dwell by the sea, and by the coast of Jordan. [30] And Caleb stilled the people before Moses, and said, Let us go up at once, and possess it; for we are well able to overcome it. [31] But the men that went up with him said, We be not able to go up against the people; for they are stronger than we.
Fear is not good when we allow it to distort our view of our great God who is greater than any problem we face.