Estimates are not commitments. More people need to understand and accept this.

You’re on the money about time and/or scope needing to be flexible. Estimates improve as you gather more information and complete parts of a project. Providing early feedback that relates to the original estimate is key!

“This is more complex because of X, and will likely add Y time. Do we want to proceed?”

Nothing worse than getting to the end of an original estimate and only then letting a project owner know it’s going to be twice as long.