Certain religions like to stress the mysterious power of ghosts and spirits. Although Buddhism does not deny their existence, it believes the biggest demon in the world is the deeply embedded tendency to cling to the self. Outer demons can only affect our daily life in small ways, such as causing illness or obstacles. They cannot bind us in samsara, not even if the ghosts of the entire universe combine their forces. Only clinging to the self has such power. Yet, we have never realized that this fellow, Self, who abides in our mind at all times and whom we are very fond of, is really a demon. If we are tired of taking the same route back to samsara again, we must first eliminate this demon. Only then can we be completely free of its interference. 

~Depicted from From Believers to Boddhisattvas