لَقَدْ خَلَقْنَا الْإِنْسَانَ فِي كَبَدٍ
laqad khalaqnal-insāna fī kabad
Certainly We have created man to be in distress (Sūratul Balad, No. 90, Āyat 4)
In the above verse Allah declares an important truth; a truth that may not be palatable to the human being. Life for human beings is often distressful and replete with travail. Man would like a life full of happiness and comfort, but apparently that is not what Allah has planned for him in this world. From the time he is born, through the stages of childhood and youth until old age, he has to undergo a variety of hardships. Human life revolves around discomforts, including physical aches and pains, mental worries, and spiritual dissatisfactions, to name just a few. This is not a bleak and hopeless view of the world, but a practical reality, and to have expectations from life that are otherwise is to be unrealistic.
Sayyid Mujtabā Mūsawī Lāri writes in his book Ethics and Spiritual Growth:
Life is like a restless sea, full of wonders and always in a state of perpetual turmoil caused by the waves of events. No one is secure from the violent waves on the surface of this deep ocean . . . Everyone who sets out on this sea is bound to be drenched by its waters and encounter in the course of his life a series of unpleasant and painful events. . .
If we think of difficulties and distress as challenges which help us rise to higher levels, we will appreciate the wisdom behind them. A human being grows through difficulties, revealing hidden colors which would never have been brought forth had it not been for the heat of trials. Imam Ali (a) says: You shall be purified in the way gold is purified. (al-Kāfī, v. 2, p.370, H. 4.) Another hadith from Imam al-Sādiq (a) says: It is inevitable that mankind should be purified, separated and sieved [through trials] (Ibid, H. 2)
Human beings love comfort and luxury. They are deeply attached to the pleasures of the senses and relish the joy of a life of ease. But too much comfort is harmful. The discomforts of life help man grow and mature. That is what Allah (st) wants from him, to progress on the path towards perfection. Islam, thus, abhors a lot of indulgence and ease. When the human being pampers himself and provides every type of comfort for himself, he becomes prone to various emotional and spiritual diseases such as pride, selfishness, immaturity, laziness, etc. It creates a rebellious spirit and a sense of self-sufficiency and inimitability, carving out a path of destruction. Evidence of this can be found in affluent societies which drift further and further away from God and the true goal of human creation. It is for this reason that we must appreciate distress, and understand the role it plays in our lives.
Sources: Āytaullāh Nāsir Makārim Shirāzī (ed), Tafsīr-e Namūneh; Sayyid Mujtabā Mūsawī Lārī, Ethics and Spiritual Growth