Risks are higher for events that have a dreaded result or catastrophic consequence. Risks in sports and occupations that have fatalities are higher than sports and occupations that don't generally have fatalities. Maturity of a technology affects risk perceptions, too. Nuclear power plants have higher risks than coal-powered plants because so much more is known about burning coal than nuclear energy. System complexity will increase risks.
Complex systems are harder to understand.
They fail in complex ways. Sometimes a failed or degraded system is difficult to detect. The more complex a system is the more important it becomes to understand the system, how it works, how it fails and learn preventative and corrective actions. The frequency and danger of an event comes from a full and comprehensive understanding of a system. Effective and accurate risk assessments should be obtained by learning about the system's operational modes.