Multiple spontaneous rhythms are present in our brain even when we are doing nothing, or at a so-called "resting state." How they functionally connect with each other and synthesize the conscious/unconscious symphonies remains as an unsolved question to modern neuroscience field. Recently, the resting-state functional connectivity was consistently reported using the typical functional magnetic resonance imaging (fMRI) technique at the resting state. This resting-state fMRI (RS-fMRI) provides detecting ability of functional connectivity across multiple brain networks and allows minimal tolerance for participants, making it proliferating in clinical and cognitive neuroscience societies. However, it should be noted that currently the biophysical mechanism of RS-fMRI continues to be entangled, and incongruous conclusion may be lead by spurious observations. In this review, two essential issues are elaborated in hope of intriguing the novel advancements on the RS-fMRI technique. The first part is the current progress in understanding mechanisms of RS-fMRI and its relationship with brain metabolism. In the second part, the practical considerations in conducting RS-fMRI experiments are mentioned to prevent careless interpretations.