Each individual person perceives the same object in a different way according to their own state of mind and projections. Everything is empty from its own side and appears according to how you see it.
Emptiness in the English language often has a negative connotation. We think of empty as void, as nothing, as lacking, as missing. This is not what it is meant in the context of yoga philosophy. Things and situations being empty means they are free from permanence. There is a subjective, flowing understanding of a situation or object, one that relies on mutual dependence.
What does that mean? If I point to a yoga mat and ask other yoga practitioners what that object is, I will get the same answer from everyone: a yoga mat. Our mutual dependence determines that this object is so. Our unwritten agreement projects this object to be the same for us. But, say, if I were to roll up the mat and take it outside the studio, and give it to homeless person, would he or she see this as an object to start doing headstands on? Not very likely. The homeless person may use this as cushion or a makeshift bed, and I will not insist that he or she is wrong for projecting the use of the object in a different way.
The yoga mat example is very tangible, and quite frankly, not that controversial. Most people would not have too many issues with the yoga mat being free from a permanent definition. But what happens when the empty nature is projected on to other things we are more invested in, like our values, traditions, beliefs, cultures, religions, politics etc? When we hold on rigidly to our own way of seeing things, to the point that we insist we are absolutely right and everyone who disagrees is absolutely wrong, we suffer. It is not a coincidence that the yoga sutra on emptiness falls under the fourth chapter, the chapter on freedom.
It is called upon us, then, that we scratch the surface of all objects and situations, that we explore and inquire and investigate and dig deeper. And we may just find that things may not appear as they are, that there is more depth, less permanence, more fluidity, less rigidity. On a practical level, think of the top-of-mind reason that brought you to practice yoga. Don't stop there though. Investigate further by asking why, why this is so, why this is important. Keep asking why and why and why, until you get to the bottom of it. In the beginning, the reason may appear to be physical, like wanting to be fit. But when you continue to ask why, you may find out it's because you want to be healthy, because you want to live long, because you want to be there for the ones you love, because you want to make sure they are okay, because the love that you have for them is immeasurable. By going deep into our own intention, we find that in our own experience, objects, situations, even intentions are not that fixed, that they are free from permanence when we allow to put them under our introspective microscope.
When we acknowledge the empty nature of everything, we will not be as motivated to create that divide between the self and others. What for? Everything is empty and subjective and ever-changing. Given this understanding, we will find more freedom in being kinder, more accepting, more tolerant, more forgiving, more inclusive, and more open-minded. Emptiness does not mean the void of nothing. Emptiness contains the richness of impermanence that it is the space to potentially include everything.