I just realized this: in the end of Transformers Prime: Predacons Rising -movie, Optimus died peacefully. For the first fucking time. Other deaths Optimus has experienced, have been violent/against his will/unexpected.
But in the TFP-movie, Optimus left with peace, by his own will and let's face it, we saw it coming. :'I
So this is what hit me hard the other day.