It is reported from ‘Alī b. Abī Tālib –Allah be pleased with him – that he said:

The thing I fear for you most is following desires and having extensive hopes (about this worldly life). Following one’s desires blocks you from the truth, and having extensive hopes makes you forget the hereafter. Verily, this worldly life is departing and the hereafter is approaching and each of them has its children. So be children of the hereafter, not children of this world, for today there are (opportunities to do) deeds and there is no reckoning, but tomorrow there will be reckoning and no deeds.

Quoted by Al-Bukhārī, Al-Sahīh, The Book of Raqā`iq without the first sentence. Reported in its entirety by Abū Nu’aym, Hilyah Al-Awliyā` Vol.1 p40, and others.

Al-Hāfidh Ibn Hajr states in Fath Al-Bārī:

Extensive hopes (about this worldly life) give rise to lethargy when it comes to acts of obedience, procrastinating with repentance, desire for worldly things, forgetfulness of the hereafter and hardness of the heart; because the softness of the heart and its purity only comes about by remembering death, the grave, reward and punishment, and the horrors of the hereafter…for if one remembers death, he strives to do acts of obedience, his worries decrease and he is satisfied with less.