Mentally forming connections with our posture is comparable to forming our qi container. For example, mentally connecting our middle fingers together and fingers to toes, etc., allows us to encircle the space that holds the energy and unite the internal line that creates continuous circulation. If these connections are not made, there will be gaps that allow the energy to escape so you cannot feel the fullness. People who practice T'ai Chi without making these connections do not get full benefits from their efforts. Like a balloon with a hole in it, the essential purpose of the movement is lost.
Air never gets inside a balloon all by itself.
It has to be pumped in from another source through a single hole. In our body, the lower dantian serves as the source of the qi. It is here that we accumulate energy, nurture it, and propel it forth. The dantian must have the continuous feeling of hollowing emptiness and accumulating fullness in order for the energy to fill the inside of your body, like air fills a balloon. Our whole body must do the same thing, like the balloon.