The presence of a legal cause does not make the required conditions irrelevant or eliminate every impediment. A cause is a basis for the ruling; a missing condition can prevent completion, and an impediment can obstruct the expected consequence even when other elements exist.
In a hypothetical contract, offer and acceptance may exist while a particular legally required condition remains unfulfilled. Proving the cause does not repair the missing condition. An independent impediment would require its own analysis even when conditions are satisfied.
Method: Separate the facts into three questions: Is the cause present? Are the conditions fulfilled? Is an impediment present? Only then draw a conclusion about application.