Background: Older adults with serious illness near the end-of-life often receive invasive treatments. We developed a conceptual model called clinical momentum that describes system-level forces producing a trajectory of care that is difficult to modify and contributes to overtreatment. We sought to evaluate the empirical fit of our model by examining an event with clear guidelines against intervention: permanent feeding tube placement in patients with advanced dementia. Methods: We screened three hospitals and identified patients 65 years and older with advanced dementia who received a permanent feeding tube. We interviewed 34 family members and clinicians. We coded transcripts and characterized factors that arose during the course of care and their relationships to feeding tube placement. We used abductive analysis to compare the data with theory and identify areas of discordance and alignment. Results: We found that the course of care started with a temporary tube to correct an acute problem. As problems were identified, multiple clinicians were consulted to address a specific problem without collective discussion of the patient's health trajectory. Eventually, clinicians had to address the temporary tube, which was framed to families as a decision to place a permanent feeding tube or withdraw treatment. Conclusion: Elements of the model-including recognition-primed decision-making, "fix-it," and sunk costs-contributed to placement of a feeding tube, which set in motion a path toward intervention long before a goals-of-care conversation occurs. Clinical momentum expands our understanding of overtreatment at the end-of-life and may reveal opportunities to reduce other nonbeneficial interventions.