Hold the hard part of the lettuce leaf (the paler, thicker side) with your non-dominant hand. Pull it in the same direction as the veins, and it should tear perpendicular to them.

[How to tear the lettuce to make it taste 10 times better] Break the lettuce leaf apart by pulling it straight outwards in opposite directions. Do not tear it like you would tear a piece of paper.

This is how normal people tear the lettuce, but it's not the right way. This way leaves a thin membrane shown in the Step 4 picture.

If a thin membrane on the surface is left behind it will make the rest of the lettuce leaf taste bad.

Please refer to "How to Remove the Core off Lettuce & How to Keep the Lettuce Fresh" too.

https://cookpad.wasmer.app/us/recipes/150730-how-to-remove-the-stalk-from-lettuce-and-keep-it-fresh