Why was it hard for bombers to take off from aircraft carriers?

Bombers were designed to take off and land on full runways with the assumption that the runway would be long enough to deal with variations in pilot skill and takeoff and landing positions.

Taking off and landing on an aircraft was not as forgiving:

• Not reaching takeoff speed at the end of the ship meant ditching in the water. There was no opportunity to turn around and try again.
• Touching down too late on the ship also could mean not stopping in time and ditching in the water.
• Trying to touch down too early meant hitting the ship.