Ecclesiastes 11:8
But if a man live many years, and rejoice in them all; yet let him remember the days of darkness; for they shall be many. All that cometh is vanity. But if a man live many years, and rejoice in them all; yet let him remember the days of darkness; for they shall be many. All that cometh is vanity.
Even if a person lives many years and rejoices in them all, he must still remember the days of darkness that lie ahead, for they shall be many. All that comes, all that lies in the future, is vanity. The warning is part of a call to the young to enjoy youth while remembering responsibility to God and the judgment that will fall upon their choices, and not to treat present pleasure as if it were the whole of life. It is Solomon's warning to the young, drawn from his regret over his own turning from God, calling them to enjoy life without forgetting its hardships and its brevity.