Understanding optimal performance of electronic circuitry

How do we evaluate automatically the optimal performance measurements of electronic circuitry? There are many new and interesting techniques for testing which crop up quite regularly. However, there must be a road map to better understand optimal performance of electronic circuitry. Optimal performance means the circuit is functioning at its' peak performance which means its' “Mean Time Between Failure” (MTBF) is the longest time between failures for the circuitry and the circuitry is optimally reliable. In other words, the test and repair process was performed by using an optimizing method thus making the MTBF high and therefore the safety of flight or the reliability of the system is enhanced.