There are a lot of things in life that I just take for granted. One of these is how a sewing machine actually makes a stitch.
I understand tensions of both needle and bobbin threads and their relationship to how that effects the actual stitch (see "Adjusting Sewing Machine Tension" to learn more).
Click on Image to see Video Illustation
I know the parts that are necessary in making a stitch: needle, bobbin, bobbin case, and bobbin hook (check your machine's manual for specific information about your machine or consider taking a class to learn).
What I didn't even put a thought into was how the machine actually made a stitch. As far as I cared, little bits of magic happened every time the needle went up and down that somehow entwined the needle and bobbin threads.
While poking around the internet, I found this video illustration that clearly shows how the bobbin hook grabs hold of the needle thread and loops it around the bobbin case. The result: a stitch.
Having seen this animation, in slow enough to see motion, it is easy to understand how threads can be entangled if the bobbin is not inserted in place properly.
Even though the video shows how a stitch is formed, I am OK with still believing that it is a little bit of magic!