Imagine you have a fish bowl and some very special marbles that shrink in size when pressure is applied. Now imagine stuffing these marbles into the fish bowl. The bowl starts to fill up. The marbles start to shrink because of the pressure. Keep stuffing more marbles. Notice they keep shrinking smaller and smaller and still fit into the fish bowl.
Now stuff an infinite number of these marbles into the bowl. What happens?
Notice that even though it's "impossible" to do that, you can still use your imagination. Use it. What do you imagine?
Now get past your imagination. What is the true nature of infinity?