When one door of happiness closes, another opens but we often look so long at the closed door

When one door of happiness closes, another opens but we often look so long at the closed door that we don't see the one which has been opened for us.这里that是不是引导从句的？ 是什么从句？

是so that 结构，如此....以至于....，that引导状语从句
当一扇幸福之门关闭时，会有另一扇门打开，但是我们总是花费很长的时间在关闭的门上，以至于我们没有看到那扇为我们敞开很久的门。

这是so...that结构，that引导的是结果状语从句。 再看看别人怎么说的。