Serial tasking is hard because switching tasks is hard, even when the tasks are easy and similar. In some experiments, bilingual speakers are asked to read out numbers, first in one language and then midway in another language. They often stumble at the switch, taking many tries before they hit their stride again.
'Serial Mom' tested really well when we finally got with the right audience. But they would go to some shopping mall in a deep, deep suburban L.A. neighborhood where they knew people would hate, and they just wanted to spend money to prove that people wouldn't like it. The movie was not a success when it came out.