Having a foot in the door is a starting point, an opportunity.

" 取得初步的成功" 就是一个新的起点，一个机会。

When you have a foot in the door, you have an opportunity to get inside a building.

当你把脚放在门上时，你就有机会进入建筑物内。

And once they developed their multi-armed, face-down body plan, starfish had a foot in the door.

一旦他们开发出多臂、面朝下的身体计划，海星就踏入了大门。