What is the most difficult part about loading a roll of film onto a reel in a darkroom?

The most difficult part is that one is loading the film in the dark.

Explanation:

Processing a film in the dark room gives photographer more control over the print and images can be easily visible to even naked eye once taken by the camera.  

There are some techniques that need to be followed in a darkroom which include dodging, burning, masking. These are more of physical techniques that need to be followed. Some of the other challenges of loading a film is that photo might come out dirty or one may break the roll while loading it on the film. There are, therefore, some safety concerns when loading a roll of the film on the reel in a darkroom.

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