situation.
this is my point,
you have to conclude or reason anything based one
the real situation.

Re-call yourself what you know when you were 20 years old,
imagine yourself if you hold a position like President Deng,
it is not difficult for you to understand that tragedy.

Naughty students with good-willing and naive ideas
made a big mess, a few ambitious guys mis-calculate
the situation so as to mis-use that movement,
the central government was forced to stop the chaos,
conflict was not avoided, tragedy happened, a few hundred
people were killed. if you wants to conclude some lessens
after 20 years, first of all, STUDENTS should not make mess by all means, it is more harm than good, government
should not worry too much about being thrown over so as to use police instead of army to stop a chaos.