It is well known that Mahabharata can be seen as an allegory for human life.
The characters of Yuddhishthira, Bheema, Arjuna, Nakula and Sahadeva are frequently discussed in this context. Even Bhishma, Drona, Dhritrashtra and Gandhari find a place in this representation.
However, I hardly found any discussion about Ashwatthama.
I feel this is important because he is at the receiving end of great suffering at the end of the war. Throughout the epic his character seems quite acceptable, except for the large mistakes towards the end. Also his immortality is a very important aspect of his character as well as his suffering.
Contemplating on this matter lead me to the possibility that Ashwatthama represents persistent doubt and criticizing nature of human beings.
Following are some thoughts that fall in line.
1) The name Ashwatthama also means a banyan tree. Branches of banyan sprout new roots which go deep in the soil. Similarly new doubts spring from existing ones and often become stronger with time. Also note banyan tree has a very long life span.
2) Ashwatthama will be alive till end of this Yuga cycle, suffering in the process, but will be the compiler of Vedas in next Yuga cycle. Doubts inspite of causing suffering and insecurity if used constructively lead to great learning.
3) Ashwatthama often doubts people around him. He doubts love of his father. He doubts Duryodhana's capability to win etc. Also note that in Kannad version of Mahabharata he is released of Krishna's curse after worshiping para Shakti. Adi Parashakti or Durga is also known as reliever of difficult and persistent doubts.
These are my musings. Would love to know views of learned readers.
Edit: Also the most important point if Parikshit is the one who is tested, then Ashwatthama is the one who conducts the test.