Is it true when your first tear comes from the left eye it means you are crying of pain?
There is absolutely no evidence at all to support the claim that there is any meaning behind which eye produces the first tear when you cry. This is a rumor perpetuated mostly on the internet.
Tears are produced in the lachrymal glands in both eyes. There's no preference based on emotion.
As a side note, when you cry, some of the tears in your eyes flow into your nasal duct, this is why your nose runs when you cry.