Iran is a country where repression is arbitrary, not systematic as in many other states in the Middle East, and it is not as efficient either. Some laws are never enforced, some murders are never solved and some critics of the regime are left alone while others are locked up. Iranians never know where the boundary is, allowing the “system” plenty of room to manoeuvre as it pleases.
Arbitrariness makes life unpredictable and allows for a degree of debate and political ferment. But sometimes it is merely cruel.