The two thirds rule of thumb emerges from typical Weibull behavior. Mechanical assets often have shape parameters (β) between 2 and 4. When service life is defined at a high reliability threshold—say, the point where 90% or 95% of units are still surviving—the ratio of mean life to service life tends to fall in a narrow band.

RUL is a condition based estimate of how long the asset can continue to perform its intended function. It’s based on degradation, inspections, performance, and failure modes. RUL is used for maintenance, risk management, and operational planning, but has nothing to do with accounting or depreciation schedules.

When we communicate asset life clearly and contextually correctly, we create shared understanding and decisions that hold up in the real world.

High-reliability organizations (HROs) build bridges between these viewpoints. They align engineering, finance, and operations so that asset decisions are defensible, practical, and focused on long-term value.