The thorns remind one of how success and happiness can be evasive and thus not to feel disappointed and disheartened rather remember that the pain of thorns is short-lived, and the beauty of life would soon overcome the prick of thorns.
Happiness, sorrow, victory, defeat, day-night are the two sides of the me coin. Similarly life is full of moments of joy, pleasure, success and comfort punctuated by misery, defeat, failures and problems. There is no human being on Earth, strong, powerful, wise or rich, who has not experienced, struggle, suffering or failure.