I read on a book that said "When you desperately want something, the universe conspires to make it happen". This sentence is about perseverance, not desire. Focusing on something for a long time is a reflection of perseverance.
Focused work gives better return
The difference of results between continuous attention and fragmented attention over a period of time is significant. With fragmented attention you will only get a superficial idea of the subject. It takes time for a mind to be submerged into something.
It's true you can a lot of work without much attention. Logistical tasks such as filling up a form or making powerpoint presentation of the sales figures do not have to be meditative.
But solving creative problems require intense attention. Works like fixing a complex bug in code, editing a research paper, writing a persuasive business proposal demand time and concentration.
Focused work is insightful
Immersing into a task gets us something else other than just getting it done. It provides insights. Insight come from deep concentration, it makes you question the why of things rather than how.
To be light is to lose one's root. To be restless is to lose one's mastery.
-- Tao Te Ching