Charles H. Spurgeon on Psalms 78:42

They remembered not his hand. Yet it must have been difficult to forget it. Such displays of divine power as those which smote Egypt with astonishment, it must have needed some more than usual effort to blot it from the tablets of memory. It is probably meant that they practically, rather than actually, forgot. He who forgets the natural returns of gratitude, may justly be charged with not remembering the obligation. Nor the days when he delivered them from the enemy. The day itself was erased from their calendar, so far as any due result from it or return for it. Strange is the faculty of memory in its oblivion as well as its records. Sin perverts man's powers, makes them forceful only in wrong directions, and practically dead for righteous ends.