Some problems get solved by thinking. Others get solved by sleeping on them.

Not every problem yields to being stared at. Some need more thinking, more information, another hour at the desk. Others are already solved somewhere in your head and are being blocked by the tiredness and the effort of forcing it, and the answer arrives while you are brushing your teeth the next morning. Knowing which kind you have saves evenings.

If you have been on something for an hour with no movement, stop and do something physical and unrelated. Sleep on it if you can. When you come back, give it ten minutes before you decide the break did nothing, because the answer usually turns up in that window.