The root cause of pain and suffering.
According to Book II of the Yoga Sutras, the 5 Kleshas are the root cause of pain and suffering.
Avidya
Ignorance, incorrect perception. Avidya points to disconnection from our spiritual selves and being totally deceived by maya or the illusion of the physical world.
Asmita
Overidentification with the ego. Asmita points to an identification with our temporary physical avatar and the egoic identity given to us and created over the course of our lives, over identifying with eternal our soul that is in unity with all beings. Asmita can lead to selfishness, an us vs. them or winners vs. losers mentality, focus on worldly things, and shame.
Raga
Attachment. Raga is our attachment to things in the physical world, with the belief that these things are which bring happiness, which is not true. Attachment can can include co-dependency on others, pleasure seeking behavior, and a lack of balance.
Dvesha
Aversion or hatred. Dvesha can be a strong emotion of avoidance of pain and anything we don't like, further emphasizing an us vs. them mentality, when ultimately we are all expressions of one spirit. There are some things we need to do on our spiritual path that we may not prefer. Growth is accepting both situations and people we like and dislike as valuable and part of the journey.
Abhinivesha
Fear of death, clinging to life, which in a way encompasses all the other kleshas because it stems from an over attachment to this avatar and the things in this life. This fear of the unknown and of death is what prevents most of us from pursuing our dreams and from simply relaxing enough to enjoy the pleasures this life can bring.
