Possible chance of abandonment because when Ty and/or the others show him mercy and kindness he seems very reluculant about it.My theory is that D-structs once had a friend but at some point before he found the crater his friend left him for reasons unknown leading D-structs HEARTBROKEN.Later on that sadness and loneliness lead into anger and hostility with the fear hidden inside of him that if he tries to open his heart to other dinotrux again he will just have it left in the dust once again.