Folding knife ergonomic design basics

A folding knife has five stages of use:

1) Draw
2) Open
3) Use
4) Close
5) Return

Each of these stages can be more or less lefty friendly.

Folding knives have evolved a lot over the last 25 years, adding features that make the knife better, easier to use, and safer. These include: pocket retention device (clip), an opening device, a blade lock. These allow a blade to be deployed and used one handed. Spyderco is the pioneer in this field, introducing the pocket clip, as well as the opening hole in the blade, and have a locking blade. Almost all their knives have these three features.
Each feature deserves its own post.