Why are there sidetracks, errors and hinderances on our path? In terms of view, it is because of the dualistic mind's clinging -- passion, aggression and delusion. These three poisons are movements of thought which are provoked by habitual patterns.
Without exception, every thought we have is mixed with these three poisons. Just as poison causes death when ingested, the three poisonous emotions take the life of Liberation when they are given free rein. We may not even notice our minds are occupied by these three poisons, which produce negative Karma. As the master -- our mind with these three poisons -- commands, it's servants, our body and voice, carry out the command. In this way, we continue roaming around in Samsara, continuously turning our back on the three kayas, which is this very basis for all of Samsara and Nirvana. Instead, we create the causes for the three lower realms.
[Tulku Urgyen Rinpoche]