The Chasam Sofer zt'l clarifies that even fear of Hashem is in Hashem's hands. It is in our hands to desire to fear Hashem and to pray for it. And when one desires and prays for yiras Shamayim, Hashem will give it to him.
The Chasam Sofer writes, "It is certain that yiras Shamayim is also in Hashem's hands because without Hashem's help, one wouldn’t attain a 1/1000th of the fear he has. (Except for the very great tzaddikim, like the avos and Moshe Rabbeinu, who didn’t need support to attain fear). [If so, why does the Gemara say that fear of Heaven is in man's hands? The answer is that] man has free will to yearn and desire to fear Hashem and to say tefillos to request that Hashem help him fear Hashem. That is up to man. The yearning and the desires aren't given from Above; a person has to work on them on his own. Therefore, the pasuk says, הימים כל אותי ליראה להם זה לבבם והיה יתן מי, 'if only they would always have such a heart to fear Me' (Devarim 5:26). It doesn’t say, אותי ויראו יתן מי, 'if only they would fear Me,' because it’s the heart and the desire that's up to man, but the actual fear is given by Hashem to those who desire it."
So Hashem does everything, and even fearing Hashem is also from Hashem. But it is our obligation to desire and pray for fear of Hashem. We will add that it is also man's obligation to avoid all matters that can destroy his fear of Heaven.
On the first night of Succos, Rebbe Yissaschar Dov of Belz zt'l asked his gabai why the soup was cold. The gabai replied that the soup was carried outdoors to the succah, so it got cold.
The Rebbe commented, "If soup gets cold by going through the city streets, what happens to a man who goes through the city streets?" The bad influences he sees and hears might cool off his yiras Shamayim, chalilah.
