95% of the board understands but him
Bloodraven took Bran into a vision of Winterfell 25-30 years in the past
He sees Hodor/Wylis when he was a kid
Bran wargs into Hodor in the present where his body still is
Somehow, Hodor/Wylis in the vision in the past, where Bran's spirit is, gets connected
Young Hodor sees and feels his own death, goes crazy, becomes retarded
He grows up into a man
Eventually he becomes the 40 year old Hodor and the past and present intersect again as this time he's the old man holding the door about to die while watching himself as a kid shaking on the ground
It's not rocket science homie. It is very simple to understand. Very simple