Sadiq has a significantly difficult time sustaining attention and completing projects that require sustained effort. These experiences are likely associated with functioning of what system?

ADHD: Attention Deficits/Hyperactivity Disorder.

Explanation:

This is a system in which a person displays inattention such as lack of persistence and lacking focus. Sadiq's inability to persevere on his projects to successful end tallys with inattention described in this ADHD.