Suffering is a Learning, and many a times occurs because of the lack of consciousness i.e. an action taken without knowing its impact, which most of the times leads to an equal or extremely opposite reaction – which tends to suffering.
Suffering is the impact that can change your action, decisions, planning and may make you change for ever.
Sufferings sometimes is because of your own deed, and sometimes, is because of your surroundings, relations, etc
Sufferings are reason that sometimes, makes you realize your faults, and sometimes makes you experience the world & its peoples.
Also, it is not always that you suffer because of your own fault, but many a times, you suffer because of doing something good for someone else.
All these level of impacts which make you reach to sufferings will also make you reach to a realization, and to achieve realization, you need to be conscious enough to understand and to take necessary steps & actions.
So, sufferings may be for any reason,
But its impact will definitely be for some good cause – either it will gives you experience or will give you an opportunity to succeed.