"have failed" is the correct option because it is in the present perfect tense, which is used to indicate that an action has been completed in the past but has a connection to the present. "Fail" is in the present simple, which is not appropriate in this context because the action is completed. "Had failed" is in the past perfect, which is used to indicate that an action was completed before another action in the past. This option doesn't match the context of the sentence, as there's no other action in the past that this is being compared to. "Was failing" is in the past continuous, which is used to indicate that an action was in progress at a specific time in the past. But this option doesn't match the context of the sentence, as the speaker is describing the result, not the progress of the action.