Let's break the task into elementary actions which we shall analyse later in detail:

• Sighting the pen and picking it up. (1)
• Aligning pen in hand for uncapping. (2)
• Feeling for the cap and aligning the thumb. (3)
• Switching to side grip after feeling that the initial grip is posing difficulties. (4)
• Uncapping and handling the cap with the rest of the fingers to fix it on the other side. (5)
• Fixing the cap on the other side of the pen. (6)
• Flipping the pen again in the palm to ready for final gripping. (7-8)
• Gripping the pen with 3-4 fingers and putting the nib/ball on the paper - ready for writing. (9)

When we use a particular pen regularly, its shape and other physical properties get registered in our mind, allowing us to maneuver this task even while not looking at it, and also while engaged in another activity. Generally many people cap and uncap a pen repeatedly several times during the day, unconscious of the fact most of the time. This is a good example of motor learning (or muscle memory). When we encounter a new pen, our hands try to open it in a way they have learnt over time. If the new pen has a different opening mechanism, then we have to actually look at the pen and use our conscious thinking to figure out how to open the pen.