being at cross-purposes from the start; getting off on the wrong foot
Idiomatic expression likening a fundamental misunderstanding or misalignment to misbuttoning a shirt from the first button. Often used when initial communication or assumptions go wrong.
See also: ボタンの掛け違い
Because there was a misunderstanding from the very first explanation, the whole project got confused.
Our assumptions were different from each other; it was exactly a case of getting off on the wrong foot.