When humans pursue two goals A and B concurrently, a part of the brain known as the medial prefrontal cortex (MFC) divides so that half of the region focuses on one task and the other half on the other task. The anterior most part of the frontal lobes enables you to switch back and forth between the two goals, i.e. executing one goal while maintaining the other one on hold. This inter-hemispheric division of labor explains why humans appear unable to accurately carry out more than two tasks at one time. If you want to look at a visual representation of how this works in the brain, I’ll include a URL below. Credit for the representation goes to principle brain researcher: Etienne Koechlin, INSERM-ENS, Paris, France.