Why did Rabbi Akiva not believe the Geula would come until he saw foxes skulking through the ruins?

The Gemoro (the last page in Maccos) brings a story that Rabbi Akiva was walking with his friends near the Har Habyis and when he saw foxes going through the ruins of the Beis Hamikdash he laughed [out of happiness]. His friends asked him why did he cry, shouldnt he be crying that foxes are in the Holiest place? He answered them that until now he wasnt sure that the Nevuah of Zecharyah that the Geula would occur would be fulfilled, but now that the part of the foxes was fulfilled so too will the Geula come as well.

Why did Rabbi Akiva doubt that Zecharay's Nevuah of the coming Geula would come? Why did he need a proof? Surely a Navi predicting it should have been enough?

Althoug I havent got an answer to this question, perhaps another question can help to answer this. The Rishonim ask how Yaacov Avinu got hurt by Esau's angel when Hashem had explicitly told him that he would be safe. The Rishonim answer that because Yaacov was scared, Hashem reneged on his promise and allowed harm to befall him. This is because the Havtacha was only there so long as there was Emunah Sheleimah.

The question that occurs now then is how do we know that Hashem has not reneged on the promise of eternal Geula because of the lack of Emunah?

Perhaps on that Rabbi Akiva is saying that the Geula has already started, indeed, the foxes are part of the eventual Geula which has already started and therefor cannot be reneged upon.

Any thoughts?