Psalms 78:42

They remembered not his hand, nor the day when he delivered them from the enemy.

The failure named is failure to keep in mind His hand and power and the day of rescue and deliverance from the enemy.
It happened although He had richly blessed His people, and it belonged to the poor return they made for all He had done for them and for His benefits.
By that forgetting they were constantly acting against a good God.
Their disobedience landed them in a condition that was the certain outcome of their own course.

Under rebuke and chastisement they repented, yet under temptation they fell again through self-indulgence and self-gratification.
When trials came their forgetting came out as complaining and losing sight of the source of their strength.
Different is the way of those who have Bible religion, with Christ dwelling in them and they in Him and truth of heavenly origin fully received, who are made holy through it and keep moving forward in the divine life rather than complaining and forgetting in trial.