The most important thing about a pair of left-handed scissors is that the left blade is always on top when viewed from above. This means that you can see the line you are cutting as you go, which is absolutely vital for accurate work. And the paper, board or material naturally moves over the thumb and under the hand to keep that clear view and accurate cut.
A lefty cutting with right-handed scissors - note the poor result.
A lefty using left-handed scissors - the line is visible and the scissors work!
When using scissors, the natural hand action is to gently push with the thumb and pull with the fingers in order to keep the blades together. Only left-handed scissors will allow you to do this when using the left hand. Using right-handed scissors in this way will cause the blades to separate and the paper will just fold between the blades without cutting! The compromise is to use a very unnatural action which will cause pain and discomfort in the short term and callus formation in the long termâ not good!
Don't be fooled into buying scissors that are labelled as "Suitable for left or right handed use" - there's no such thing! They are just right-handed scissors with a grip that feels comfortable when used in both hands but the problem remains: they are not left-handed scissors! And it doesn't work turning a right-handed pair of scissors upside down either - they are still right-handed scissors!
Try a real pair of left-handed scissors and you'll wonder why you ever put up with the discomfort.