Why are contrails not visible from the cabin? If you observe a plane flying whilst on the ground, plenty of times you will see contrails:



Why are they not visible from the plane itself when sitting in the most rear part of the cabin even by trying to look towards the rear of the plane fuselage? They seem to be quite close to the engines.

Knowing that they form due to the heat, they should be seen quite close to the engine.
The distance between the engine and the start of the contrail depends on:


the engine type
the temperature of the outside air
the moisture content of the outside air. 


Usually the contrails don't form before the tail of the aircraft, but in extreme cold or humid air contrails can be seen forming just behind the wing. 

On larger aircraft you have a better change of seeing the contrail from inside the aircraft. On the 747 you can often spot them for the window of the rear passenger door.