What is meant by Sufyan's saying: "Weeping is ten parts: one for Allah, and nine for other than Allah. If that which is for Allah comes once a year, it is abundant"?

This statement was quoted by Al-Dhahabi in Siyar A'lam al-Nubala' from Abu Ishaq al-Fazari, who reported that Sufyan al-Thawri said: "Crying is ten parts: one part for Allah, and nine parts for other than Allah. If the part that is for Allah comes once a year, it is a lot." Sufyan's words indicate that sincerity in crying is rare, and that one who cries out of fear of Allah with sincerity is among the seven whom Allah will shade in His shade on the Day when there is no shade but His.