Exploring and advancing the fifth hand principle of project behavior: Lessons from Denmark’s tax governance project

• Project processes are uncertain and driven by side effects • Succes in capacity building projects is complex and ambiguous. • Coexistences of the benevolent Hiding Hand and the malevolent Hiding Hand • Testing of new theorisation through the Fifth Hand • Tax Governance as capacity building within tax administration This study explores and advances the Fifth Hand principle of project behavior, a recent theoretical approach that accommodates the contradictory explanations of project behavior—Flyvbjerg's Planning Fallacy and Hirschman's Hiding Hand (Ika et al., 2022; Love et al., 2022). While the principle has been conceptually developed, its empirical applicability remains unexplored. This study addresses this gap by analyzing a capacity-building project conducted by the Danish Tax Authority. The findings reveal the coexistence of contradictory project behaviors which leads to the existence of both failure and success in the project depending on the macro- and micro-level perspectives. The study contributes to the advancement of the Fifth Hand principle, by providing an empirical exploration and by offering insights into how contradictory behaviors are accommodated in projects. The contributions are conceived by paying close attention to the lived experience of managing projects in practice.