“The saints, too, had wandering minds. The saints, too, had constantly to recall their constantly wandering mind-child home. They became saints because they continued to go after the little wanderer, like the Good Shepherd.”
– Peter Kreeft
 
Kabir – The couplet
सुमिरन की सुधि यूँ करो, ज्यों सुरभि सुतचहि ।
कहहि कबीर चर चरि,सुरभि बच्चुके पाहि ||

Transliterated:
Sumiran Ki Sudhi Yun Karo, Jyon Surabhi Suthchahi |
Kahahi Kabir Char Chari, Surabhi Bachchuke Paahi||

Translation:
Practice meditation in this fashion, like the cow grazing on grass |
Even as its teeth tear up the crass, its attention stays focused on its calf||

My understanding:
In anything as relative as human life, there can be no absolutes. From there follows the thought that absolute focus is not an initial reality – not at least till we have stepped beyond the self-doubt that continues to plague us at all times.

So how do I overcome the eventual drop of focus? By learning to recognize the telltale signs of faltering focus, and then taking appropriate corrective action. Endless distractions keep our self from focusing on a task as we struggle to get anything done. The simple answer to keep out distraction at bay is to point our attention to the one thing, completely ignoring the other things around until nothing else can find a way to come into focus.

Just as a clean space invites you to do work there, a clean mind allows for better focus. So de-clutter the mind. Recognize extraneous thoughts for what they are, and discard them. Do not file them away – trust the brain to be able to repeat conjuring up that random thought again when the need arises. Learn to tag, trash and dispose of garbage thoughts as soon as they show up. They not only clutter up the environment, they make the space unpleasant, and their odor drives away all sense and sensibility. We do not keep smelly garbage around the house – why then this morbid craziness that makes us retain all of those really disturbing memories and imagined moments? Get rid of them.

Maharishi Patanjali said:
ततः पुनः शातोदितौ तुल्यप्रत्ययौ चित्तस्यैकाग्रतापरिणामः |
tataḥ punaḥ śātoditau tulya-pratyayau cittasya-ikāgratā-pariṇāmaḥ |

The transition to one-pointedness, or ekagrata-parinamah, is the transition whereby human mutability (chitta) becomes perfectly balanced between arising and subsiding.

Focus on the joy you will find at this point, and use the energy generated by that expectation to keep the disturbances at bay.