I'm right-handed, and usually use scissors with my right hand. When I try using them with my left hand, two things happen: First, they doesn't sit right in my palm, because of the way they are sculpted. Beyond this, and more importantly, they are no longer as effective in cutting things.
Here's my understanding of why this is. When holding the scissors with your hands, in addition to the up-and-down force you exert on the blade with your fingers, you also exert a small side-to-side force with your fingers. With my right handed scissors in my right hand, this force pushes to the outside on the upper handle and to the inside on the lower handle. This force also makes the scissors feel more comfortable.
On the other side of the fulcrum, though, the upper handle controls the lower blade and the lower handle controls the upper blade. Here, the lateral forces end up drawing the blades closer together, giving a tighter pair of edges between which shearing forces are applied. This makes the cutting action more effective than if lateral forces were absent.
In my left hand, the (outside at the top and inside at the bottom) lateral forces end up pushing the blades further apart on the other side of the fulcrum. This reduces the shear force and makes the cutting action less effective.
To compensate for this while operating the scissors with your left hand, you would need to adopt a weird style: Consciously pull to the inside with your thumb, and to the outside with your remaining fingers. You'll notice that the scissors are now much more effective than before. It is also a deeply uncomfortable grip.
The issue is that scissors are (surprisingly) chiral sculptures. In the case of regular right-handed scissors, when viewed edge down, the handle closer to the viewer passes through the left of the fulcrum. I have never used a pair of left-handed scissors, but I would presume that for them, the closer handle passes through the right side of the fulcrum.
This is exactly right. Scissors depend on you to exert sideways pressure on the blades. It should be possible to build scissors with e.g. a spring at the joint that exerts the proper sideways force automatically. This is how paper cutters work. (A square surface with a blade on the side that swings down.)
Here's my understanding of why this is. When holding the scissors with your hands, in addition to the up-and-down force you exert on the blade with your fingers, you also exert a small side-to-side force with your fingers. With my right handed scissors in my right hand, this force pushes to the outside on the upper handle and to the inside on the lower handle. This force also makes the scissors feel more comfortable.
On the other side of the fulcrum, though, the upper handle controls the lower blade and the lower handle controls the upper blade. Here, the lateral forces end up drawing the blades closer together, giving a tighter pair of edges between which shearing forces are applied. This makes the cutting action more effective than if lateral forces were absent.
In my left hand, the (outside at the top and inside at the bottom) lateral forces end up pushing the blades further apart on the other side of the fulcrum. This reduces the shear force and makes the cutting action less effective.
To compensate for this while operating the scissors with your left hand, you would need to adopt a weird style: Consciously pull to the inside with your thumb, and to the outside with your remaining fingers. You'll notice that the scissors are now much more effective than before. It is also a deeply uncomfortable grip.
The issue is that scissors are (surprisingly) chiral sculptures. In the case of regular right-handed scissors, when viewed edge down, the handle closer to the viewer passes through the left of the fulcrum. I have never used a pair of left-handed scissors, but I would presume that for them, the closer handle passes through the right side of the fulcrum.