Abu al-‘Ala relates: The Messenger of Allah ﷺ said, “Verily, Allah will put His servant to trial in what He gives him. Whoever is content with what Allah has apportioned for him, then Allah will bless him in it and expand it. Whoever is not content, he will never be blessed in it.”
(Musnad Aḥmad)
Man’s life is full of trials. This is as per the divine scheme. Allah puts humans to trial in various ways. Some persons are put to trial in the bounties and abundance of provisions that Allah has blessed them with. Some other persons are put to trial in their sufferings and deprivations. In all situations the believer needs to stand steadfast in his faith (Iman) and be thankful to Allah for whatsoever blessings of Allah remain with him, even for the breath he takes and ultimately for being steadfast while passing through trials and tribulations.
Allah is All-Powerful and All-Knowing. But he puts man to trial to ascertain, through his own deeds at difficult times, whether or not he is contended. The hadith says that Allah increases His blessings for the person who remains steadfast and contented while facing trials and tribulations. This is how Allah rewards a contented soul here on earth, and whatever He will give him in the Hereafter will be much greater than what He has blessed him with on earth. This is in fact success.
On the contrary, whoever fails to remain contented at difficult times, he will not be blessed in it. This will be failure for him.