# The ability to divide attention depends on difficulty of the task
This can be understood from Perceptual load theory. When a task is so hard it consumes all of our attention capacity, we'll not be able to use our attention for anything else.
# References
Goldstein, Cognitive Psychology (p. 109).
An example of divided attention becoming difficult when the task is made too hard is actually provided by driving. You may find it easy to drive and talk at the same time if traffic is light on a familiar road. But if traffic increases, you see a flashing "Construction Ahead" sign, and the road suddenly becomes rutted, you might have to stop your conversation to devote all of your cognitive resources to driving.