Deuteronomy 4:9 (NKJV)
9 "Only take heed to yourself, and diligently keep yourself, lest you forget the things your eyes have seen, and lest they depart from your heart all the days of your life. And teach them to your children and your grandchildren,
Deuteronomy 6:10-12 (NKJV)
10 "So it shall be, when the LORD your God brings you into the land of which He swore to your fathers, to Abraham, Isaac, and Jacob, to give you large and beautiful cities which you did not build,
11 houses full of all good things, which you did not fill, hewn-out wells which you did not dig, vineyards and olive trees which you did not plant--when you have eaten and are full--
12 then beware, lest you forget the LORD who brought you out of the land of Egypt, from the house of bondage.
Deuteronomy 8:11 (NKJV)
11 "Beware that you do not forget the LORD your God by not keeping His commandments, His judgments, and His statutes which I command you today,
You just read about people who forgot about God. They just went about their lives never thanking him for the things they have. Look around you. Everything you have comes from God. Don't forget him. Don't forget to thank him.
Hebrews 2:1 (NKJV)
1 Therefore we must give the more earnest heed to the things we have heard, lest we drift away.
Judges 8:32-34 (NKJV)
32 Now Gideon the son of Joash died at a good old age, and was buried in the tomb of Joash his father, in Ophrah of the Abiezrites.
33 So it was, as soon as Gideon was dead, that the children of Israel again played the harlot with the Baals, and made Baal-Berith their god.
34 Thus the children of Israel did not remember the LORD their God, who had delivered them from the hands of all their enemies on every side;
Psalm 50:22 (NKJV)
22 "Now consider this, you who forget God, Lest I tear you in pieces, And there be none to deliver: