People who have ADHD are more likely to experience difficulties with the attention blink test. Due to their difficulty to stare at a fixed space and attention deficit they miss more letter sequences.
To put this into perspective, this can be applied to the real world for any given person in circumstances such as if a driver in front of you is swerving off the road, you will briefly become focused on that catastrophe (attention blink) in the making and lose sight of the specific details of the traffic around you in that moment. I can only imagine how difficult it may be for a student in a classroom that is not on ADHD medication and is trying to pay attention to a lecture but sees phones lighting up with notifications or hears students talking outside in the hallway.
As someone who has ADHD (not on medication) this makes sense to me. When doing the attention blink test on the Zaps program used in my Cognitive Psychology class there was a continuous stream of 80 different tests. I found myself fidgeting in my seat and having to take breaks. It made me feel irritable and impatient and I had a hard time finding the first letter in the sequence for the first few trials. Eventually I sort of picked it up but I struggled finding a second letter in the sequence.