To portray sorrow on screen, you do not necessarily need to have a tragedy in your life. You can see it happening to others. You can learn from them, from books and other movies you see.
When I have to portray sorrow, I cross my fingers and say 'God I don't want this to happen, I am just imagining it, please don't let it happen.' I then enact the scene.
Drawing the right line between being natural and yet deliberately adding the right nuances for the camera is what acting is all about.
Though my first language is English, I have no problems acting in Hindi movies. The real problem was acting in Bengali. There, I had to learn the script by heart. That's different from understanding your lines and speaking it. It's more difficult when you have to learn it by heart. You have to stick to the script.
When you understand your lines, you do not have to do it word for word.