Attention is limited, and you can feel the limit. Effortful thinking has a cost: it slows you down, narrows your focus, and competes with other tasks.
The slow system is capable, but it is a scarce resource. When it is overloaded, errors rise, self-control weakens, and you fall back on default routines.
Because effort is costly, you naturally avoid it. You simplify, you rely on memory, you accept plausible stories. Even when you intend to be careful, the mind quietly looks for shortcuts.
This makes vigilance situational. In a calm moment, you can reason well; under pressure, fatigue, or distraction, you outsource judgment to automatic impressions.
If you want better decisions, you have to treat attention like a budget—spent deliberately, protected from needless drains.