People mentioned already how the overload, responsibilities and distractions that only multiply with age make it difficult to allocate sufficient energy and focus to get a strenuous mental task done. This is much easier when younger. I recall spending long stretches of time reading e.g., a book front-to-back. I don't think the reason I am not doing this anymore is due to declining mental ability. During the pandemic on occasion this has happened again :-)
One simple trick that works for me sometimes is to create a "clean room" for the brain: e.g. change work environment and/or isolate for a fixed period pushing all other deadlines further out. Remove the external pressure and allow time to get into flow.
Ofcourse it might be that what you have to do is materially more difficult than previous tasks you handled. Using mental support tools (notes, diagrams etc) might bring it back within reach.
One simple trick that works for me sometimes is to create a "clean room" for the brain: e.g. change work environment and/or isolate for a fixed period pushing all other deadlines further out. Remove the external pressure and allow time to get into flow.
Ofcourse it might be that what you have to do is materially more difficult than previous tasks you handled. Using mental support tools (notes, diagrams etc) might bring it back within reach.