In 2017 Jacinda Ardern's very first promise as Labour Leader was that Labour would build light rail to Mt Roskill by 2021. Previously Labour had a more realistic policy of within a decade, but Ardern needed momentum so they presumably just made up a new date and announced it. And Aucklanders believed her.
In 2020 Labour again promised light rail in Auckland.
Now we find out that construction won't begin until at least 2024. So they promised 13 kms to be complete by 2021, and the reality is they won't even start until 2024.