Sunk-cost effect — Arkes & Blumer (1985), Organizational Behavior and Human Decision Processes: ten experiments + theater-season-ticket field study (full-price buyers attended more plays than discount buyers); MONETARY robust, time/effort weaker

Claim: The sunk-cost effect is the tendency to continue an endeavour because of prior irrecoverable investment of money, time, or effort — even when forward-looking analysis says to stop.

Arkes & Blumer (1985) demonstrated the effect across ten experiments plus the famous theater-season-ticket field study: people who paid full price for season tickets attended significantly more plays than those who received random discount cards — even though the marginal cost of each play attended was identical for both groups.

For new-site owners: the more they have already spent (on the new site, the new brand, the new content), the harder it is to walk away — and the more they are vulnerable to pouring additional money into a structurally broken site.

Source: Arkes, H. R., & Blumer, C. (1985). "The Psychology of Sunk Cost." Organizational Behavior and Human Decision Processes 35(1):124–140.

Confidence: Verified for monetary sunk costs in lab and field. Single-source/Directional for purely behavioural (time/effort) investments; Soman (2001) and some failed replications find the effect weaker or inconsistent there.

Caveat: Pair with Rule: watch for BOTH sunk-cost escalation (pouring money into a structurally broken site) AND hyperbolic-discounting abandonment (quitting before a slow payoff) — the discipline is the same: judge on evidence accumulated over the pre-set window — sunk cost pushes toward over-investment; hyperbolic discounting pushes toward premature abandonment; the discipline against both is the same (judge against the pre-set measurement window).