[throwaway823882]

Which bias, the bias to want to multi-task? It's not a bias, we're just stupid. We think we can do multiple things at once. And we can do multiple things at once, so our stupid brains have proof that we can multitask.

The problem is that humans can't objectively qualify their own results without analysis, and we don't do rigorous scientific analysis on ourselves regularly, so we have no idea when something we do is shit or not. The only facility we have for that is comparison and pattern recognition, which is not rigorous analysis. If you don't go out of your way to compare your results as a multi-tasker to the cumulative qualitative results of somebody else doing two different things, you will never see that multi-tasking is worse.