Fear

Fear is an ally. Fear can be a weakness.

Fear will attract everything at some point in some manner. It is inevitable.
While it attracts everything, more specifically it attracts people that are generally fearful, and that same fear attracts the strong. People who are fearful are weak. People that live with fear can have those fears exploited. It is a weakness, not a strength.

Fear can hold people back, and this is a weakness.

A perfect Sith has no fear. However, there is no person that lives with no fear of some sort. People with high levels of fear do not take risks, and therefore never get what they want out of life. A person who takes those risks overcomes their fear. Fear is no longer an issue for them. A person with few fears is bound to be successful. Fear is an ally to those who are strong.

But having fear does not mean that you voice it to the world. You have to keep it internal, confront it, conquer it. Once fear is conquered, you are limitless.

Fear. Fear attracts the fearful… the strong… the weak… the innocent… the corrupt. Fear. Fear is my ally. - Darth Maul