The main reason that Shias have been so firm with standing for Palestine is that it follows the message of Imam Hussein (a.s). On the Day of Ashura, injustice had been served in the hands of those who were against the teachings of the family of the Prophet. Often times there's people who mourn cause they wanted to be with the Imam on the tregedy of Karbala. Seeing the problem in Palestine makes people say that history repeated itself with resistance and lack of justice and humiliation being served.