I received this little video today from a very kind gentleman, and I just had to share it with you! Neither of us can find the originator of it, but it's not from lack of trying.... This displays how a stitch is formed. You can see how the rotary hook spins around, capturing the thread from the needle, and actually forming the stitch. If your top tension is too tight, the rotary hook cannot form the stitch, and you will have skipped stitches throughout your quilt top.