Ah yes, the thumb. I figured I should devote at least one feature into determining the truth behind what constitutes a good thumb from a bad thumb.
Whenever I get ahold of a thumb that fascinates me, I am stuck with a feeling of awe, the thumb seems to eminate some kind of power, a mighty stature with bold features and a confident demeanour, an instrument of ingenuity. If you look to the image, you'll see an example of such a thumb. I'm going to let the thumb bask in anonymity and let you focus on the fact that it's a thumb, not who it belongs to.
As you can see, the digit is extended. The actual base of the thumb, where it protrudes from the rest of the hand, is where the magic starts. Beautifully toned hand muscles support the upper part of the thumb, and if we look further up, you'll see the bottom knuckle in all its glory. The middle knuckle carry the wrinkles that we all adore so, and resting majestetically upon the very end of the thumb is the thumb nail, which nearly deserves a chapter for itself. Looking at the picture we see can see how it arcs across the nail bed, perfectly buffed and taken care of. All of its aspects put together, this thumb is a prime example of one that instills awe in me, and it has the potential to be one of the best parts of any hand. In this hand it may very well be.
While the criteria for a good thumb may be fuzzy, there's a gut feeling that lets me differenciate between the two. A bad thumb might be disproportioned, have a short of neglected nail, or even have unnamable qualities that makes it look weak and puny.
All in all, I can safely say that the thumb is one of my favorite digits, and I hope I've sparked your interest for thumbology with this feature. ;)