When you're separating the celery leaves from the stalks, carefully bend the part right under the leaves from the curved inside to the straight outside.
The strings connect the two parts, so gently pull the leaves down the stalk and the strings will come with them.
Story Behind this Recipe
I have started cooking celery more often since I came to the States. When I uploaded celery recipes, people sometimes commented that de-stringing celery is troublesome, so I uploaded this method to teach you how to de-string it easily.
As long as you pull down the leaves slowly, the strings will come off easily. The key is de-stringing from the top to the bottom. If you do it in a wrong direction, they will rip halfway through.