Focus on what matters, filter out the rest.
Selective attention is your brain's ability to lock onto one piece of information — a task, a voice, a colour — while filtering out competing input around it.
Almost every task that requires concentration depends on this: reading in a noisy room, following one conversation at a party, or picking the important line out of a busy screen.
ADHD brains often process many stimuli at a similar intensity, which can make it genuinely harder to automatically suppress the "noise" and stay locked onto one target — not from a lack of trying, but because the natural filtering happens differently.
Trying to read an email while a notification banner, a conversation in another room, and a half-finished thought are all competing for attention at once.