A casual conversation with a friend of mine on why animals can't speak made me recollect at once a story narrated by my grandmother in my childhood. Yamraj, the god of death was at the doorstep of a person to take him from the earth. As the man was having his supper, he waited outside the house as it is unfair to take a person while having food. The cow which belonged to the house owner gave a message to him that Yamraj is waiting outside and he shouldn't stop having supper so that he can escape from his clutches. Yamraj became very angry and cursed the cow: "From today, you will be dumb.". From that day, all the animals became dumb.
Not one, our history is replete with instances of CURSE changing the course of life. The Bhagavat and the whole family story of Lord Krishna starts with a curse on King Parikshit by a saint and ends with a curse on Krishna by Gandhari. The Mahabharata and the Ramayana will give you at every point an incident of curse. We can't imagine what course these stories would have taken without CURSE. You will be surprised to find that CURSE played a more vital role in changing lives than blessings.