Samskaras are the tracks or Scars left in the Astral/ Emotional Body, the energy surrounding the physical body, which is called the Auric Field.
Major Samskaras are developed over one or more previous lifetimes. We tend to draw to us that which we fear. It follows that if we have a tragedy in one lifetime, the fear of this happening again adds to the likelihood of the tragedy repeating itself, hence a major Samskara. If these Samskaras are not dealt with in a proper manner they can cause dis-easment in the physical body. Pain that recurs in a particular spot with no physical explanation can be the result of a Samskara that has come up for release.
We create Samskaras in our present life. One of the criteria for a Samskara to be imprinted on the Auric Field is the power of the emotion at the time the incident occurred. Example: A child is bitten by a dog and from then on fears dogs. (Strong Emotion) When she meets another dog her fear attracts another attack thus reinforcing the fear/scar/Samskara.
In our quest for spirituality our Samskaras are our main deterrent. As Samskaras that are not cleared mimic the emotion at the time of the event we find ourselves being triggered to exhibit an emotion that is entirely out of proportion to the event at hand. We can repeat any emotion adnauseam, bitterness, anger, fear, etc. until we have cleared off the Samskara that caused it.