"It runs" is the floor, not the goal. A project that ships on time but nobody uses, or that works today and pages the team every night, is not a success. As a tech lead, you define what success means up front, with stakeholders, so the team builds toward outcomes rather than just toward "done."
Agree on success metrics with stakeholders before writing code. "We'll consider this a success if adoption hits X and p99 latency stays under Y" turns a vague goal into something you can actually measure, and prevents the post-launch argument about whether it worked.
Teams that measure success only as "shipped" optimize for the wrong thing: they celebrate launches that quietly fail in production or with users. A tech lead who defines success across all these dimensions steers the team toward work that actually matters, catches problems while they're still cheap to fix, and can show leadership concrete evidence of impact rather than just activity.