How do you handle disagreement with a co-worker?

Situation: A senior colleague advocated for a single monolithic dbt project; I favored domain-based multi-repos. We were at an impasse before a major migration. Task: Reach a decision that served the team without creating resentment. Action: I proposed a timeboxed spike: prototype both approaches for one domain and measure—build time, test latency, merge conflict frequency. I documented both options in a shared doc with pros/cons and assumptions. We ran the spike over 3 days. Results favored multi-repo for our scale (12 engineers, 50+ models). I shared findings in a team review; we adopted multi-repo. I made sure my colleague's concerns (discovery, consistency) were addressed in the design. Result: We shipped the migration on time; the colleague later became an advocate for the approach. Pro tip: Data beats opinion—prototype when stakes are high.