What is deep work?
Work that requires your full attention for an unbroken stretch: thinking, building, writing, planning, solving something that does not yield to a quick answer.
The opposite is not laziness. It is shallow work, which is real and necessary and often urgent, and which almost never moves anything forward on its own.
Why can't it be done in gaps?
Because attention takes time to reach depth and loses it instantly.
A man settles into a hard problem after roughly twenty minutes. One interruption and he is back at the start. Four interruptions in two hours means he never once got to the part where the work actually happens.
This is why a day can be full of effort and empty of progress.
Where do the hours go?
The phone, mostly, and not for the reason men think. The problem is not minutes lost to it. It is that checking it resets the clock on depth.
Then meetings that could have been a message. Then the habit of answering immediately, which feels like being conscientious and is really being available at the expense of being useful.
How do you get it back?
Two hours, one subject, phone in another room, at the same time every day.
The time of day matters less than the repetition. A man who protects the same two hours daily gets more done in a month than he did in the previous six, and it stops requiring willpower somewhere around week three.