The proper needle will fall down into the hole of your canvas and catch at the eye of the needle, or fall all the way through. If the needle is patted or pushed down into the hole, the needle has made the canvas holes displace, disturbing the weave of the canvas. This will cause uneven stitches and warping of the canvas. Working thread lengths should be 18 to 20 inches or, as an easy measure, from the tip of your middle finger to the bend of your elbow. Long threads wear the nap off and get too thin as a result of passing through the canvas holes too many times.
All threads wear and get frizzy at the needle's eye from pulling through the rough canvas.
They may be stitched simultaneously if the areas are well divided.