Know and mark the edges of your circle

Label the boundary clearly: 'inside my circle’ vs 'outside my circle’ vs 'I am not sure.'

Why it works

An unmapped edge is invisible and therefore crossable without warning. Explicitly marking the boundary — "I know retail banking well; commercial real estate I only know the surface of" — creates a cognitive speed bump before decisions in adjacent territory. The edge is where confidence is highest and accuracy is most likely to have diverged, making it the most dangerous point in the circle.

How to do it

1. For a domain, ask: what are the adjacent areas where my knowledge starts to thin?
2. Write a one-sentence description of where your knowledge ends for each major area of your work or life.
3. When a decision touches an edge area, flag it explicitly before acting.
4. Treat edge-area confidence as a warning sign, not a green light.

Evidence

Research on overconfidence shows it is highest in novel, adjacent domains — where the thinker knows enough to feel confident but not enough to know what they are missing. Experts in one field routinely overperform their actual knowledge when reasoning in adjacent fields. Tetlock's (2005) long-run study of expert forecasters found that experts operating beyond their core specialty were systematically overconfident, empirically locating the danger at the edge. (observational)

The specific mechanism of "edge overconfidence" is a principled extension of overconfidence research rather than an independently studied phenomenon.

Sources

• Lichtenstein, S., & Fischhoff, B. (1977). Do those who know more also know more about how much they know? Organizational Behavior and Human Performance, 20(2), 159-183.
• Tetlock, P. E. (2005). Expert Political Judgment: How Good Is It? How Can We Know? Princeton University Press.

Common mistake

Treating the edge as a gradient to push rather than a boundary to mark — continually rationalizing why the adjacent area is "close enough" to your core domain.