What were the difficulties faced by the horse during his life? How did he overcome them?

The main difficulties Black Beauty faces include service under cruel or ignorant caretakers, illness, injury, separation from friends, and loss of freedom to roam/graze. The ways in which Black Beauty deals with these difficulties include commiserating with friends, remembering the happiness of his youth, and hoping for better days ahead.
After coming of age, Black Beauty is separated from his mother and sold to Squire Gordon. On Gordon's estate, he enjoys a safe, comfortable lifestyle. Gordon hires knowledgeable caretakers to tend his horses, and Black Beauty shares the stables with several horse friends.
Though the Squire's pasture is well-tended and his horses well-treated, Black Beauty dislikes working for humans day in and day out. He misses the carefree freedoms of childhood—the freedom to graze free for hours and the comforts of being near his mother. Black Beauty deals with this difficulty by befriending his fellow stable horses, Ginger, James, Merrylegs, and John Manly. By sharing stories of his childhood and hearing his friends' stories, he is able to better cope with his current situation.
Later in life, Black Beauty sustains severe injuries due to the negligence of his riders and caretakers. Throughout his struggles, he shares his pain and suffering with his friends, especially Ginger. This strong friendship provides a means of support as Black Beauty experiences human cruelty and neglect. As he begins to age, Black Beauty also starts to look forward to retirement. He hopes to come under the care of a kind and knowledgeable owner. These hopes for a better future help Black Beauty to cope with his current difficulties. Ultimately, he does retire under a kind and knowledgeable owner. Thus, Black Beauty is able to live out his days in comfort and peace.