The sense that sustained concentration has become harder is widely reported. The mechanism is less about damaged attention spans than about an environment built to interrupt them profitably.
Attention is a selection process
The nervous system receives far more input than it can process, so attention functions as a filter that promotes some signals and suppresses the rest.
Suppression is active work. Holding focus on a task means continuously inhibiting competing signals, and that inhibition draws on limited capacity.
Which means concentration is not a passive state that simply persists. It is maintained effortfully, and it degrades as the effort accumulates.
Novelty overrides the filter by design
Certain signals bypass voluntary control. Sudden movement, a new sound and anything unexpected capture attention automatically, because missing a genuine change was historically expensive.
Notifications are engineered to imitate exactly those properties, arriving unpredictably and signalling something new. The involuntary system responds before any decision is made about whether to engage.
This is why willpower is a poor defence. The capture happens ahead of deliberation, and the decision being made is whether to return, not whether to look.
Switching has a measurable cost
Moving between tasks requires reloading the relevant goal, rules and context. That reconfiguration takes time and leaves residue from the previous task interfering with the new one.
A brief interruption therefore costs far more than its own duration, and the deficit is largest for complex work where the reloaded context is extensive.
Frequent switching across a day produces a pattern of consistently shallow engagement, which is experienced as an inability to concentrate rather than as an interruption problem.
Variable reward keeps checking alive
Feeds and inboxes deliver something interesting unpredictably. Rewards on an irregular schedule sustain a checking habit far more effectively than reliable ones.
Under that schedule the behaviour continues through long unrewarded stretches, because the next check might be the one that pays, and there is no signal that it will not be.
The habit then runs without a conscious trigger, which is why people find themselves having opened an application without any memory of deciding to.
Environment beats intention
Because capture precedes choice, changes to the environment are more effective than resolutions about behaviour. Removing the source of interruption removes the contest entirely.
Working in blocks with a defined end also helps, since the demand on inhibition is bounded and the system is not asked to hold indefinitely.
Where difficulty concentrating is longstanding, extends across every setting and predates the current environment, it is worth discussing with a clinician rather than treating as a habit problem.