I listened to an interview on NPR with someone else who was a leader on JWST and the host asked this leader if there was ever a time when it all felt hopeless, that things were doomed to fail. The leader said: no, never. When they encountered a major issue, or a costly mistake was made, the team did not despair or point fingers. Instead, they just added time to the schedule, and worked to figure out how to solve the issue and move on to the next problem. This person also noted that pretty much everyone involved felt they were working towards the greatest achievement of their lives.