It keeps us from harm. No one likes to be burned twice, So we can take that experience though it may have hurt,but through that you can apply your struggle to the next hardship that occurs in your life.
It strengthens relationships. If your life is always going good it would be almost impossible for people to uphold tight relationships. With out trials no ones bond is tried,and if it is never tried you never know if it's something worth keeping.
Suffering reveals a lot about a persons character. Wether they are a patient person,an angry person,a violent person? With out struggles we would look more like dolls than human beings.