Imagine you have a software need that two contractors are working on. One says it will take 2 years. The other says 2 months, and says they are writing code faster.
One project started in 2007 planning activation in 2025 and planning reactions in 2035. The other started in 2015, activated 2017 and steady state reactions have been delayed from the original Sept 2021 plan to 2022. It's not even close the results so far.