Whilst possessing a genius like ability from an early age, it still took considerable practice in order for Albrecht to master the human form. Other masters were the same, see drawings by Michelangelo and Da Vinci for examples of just how much time was needed in order to meet this considerable challenge.
Such study pieces were never intended to be displayed as artworks in their own right and so many featured several different sketches together on the same slip of paper. This allowed an artist to maximise his sketchpads as well as compare his different creations more easily. In some cases they would actually draw on both sides of the paper, with no intention to ever have it framed.
If you take a closer look at the fingers themselves, certain elements don't quite look right. The thumb that is held by two fingers seem angled wrongly whilst a small finger on another hand seems added on as an after thought. Clearly practice was needed and Durer knew it. There is no shame in this, though, as all went through a similar process of experimentation and perfection.