How does overall system reliability relate to the least reliable component in a series system?

In a series system, the overall system reliability is determined by the product of the reliabilities of each individual component. Since all components must function correctly for the system to work, the overall reliability cannot exceed that of the least reliable component. If any one component in the series fails, the entire system fails, making the system's reliability inherently less than or equal to the reliability of the weakest link, or the least reliable component.

This is why it is correct to state that the overall system reliability is less than the reliability of the least reliable component. The least reliable component essentially becomes the limiting factor in determining how well the entire system can perform. Thus, if you have a series of components where one component has significantly lower reliability than the others, that component will dictate the maximum reliability of the entire system, leading to a situation where the system's reliability is less than that of the least reliable part.