it definitely depends on the moment each type of adhd will have different struggles but essentially its not knowing what to pay attention to its either hyperfocus or distractions - my therapist likes to explain it as us being in a room with hundreds of tvs all on different channels and we dont know which one we are supposed to be watching   we also have an interest-based nervous system so we cling onto what we are most interested in  passionate about and when we do things we dont want to do as much our attention can be disrupted much easier