How can one balance between the fear of Allah and a bad ending, and having a good opinion of Allah and enjoying life, in order to overcome the whispers of Satan?

The praiseworthy fear of the Day of Judgment is that which motivates righteous deeds, not despair, negligence, or doubt, for this fear is mixed with hope and good expectation of Allah. Sadness is not among the desired stations; indeed, the Quran has forbidden and negated it, because it halts the seeker from his journey and weakens the heart, and it is beloved by Satan. Fear should not exceed its bounds to despair of Allah's mercy; rather, it should prevent one from committing sins. The blameworthy fear that leads to despair is a sign of ill-manners towards Allah's mercy. A Muslim should make his fear a motivation for diligence in study, honoring parents, and benefiting Muslims, and he should avoid the whispers of Satan by returning to Allah.