Autosomal DNA's random inheritance pattern can be difficult to understand. If you're a visual learner like I am, well...we need a visual.
Let's assign each of our ancestors a different color and assign the DNA they pass on to us the same corresponding color. If we visualize this inherited DNA as confetti and watch our ancestors toss this confetti into the air, this happens:
Some of us descendants might have pink confetti and green confetti but no purple land on us. Some might have red but no yellow or orange land on us. Others might have blue, pink, orange, and green but no red confetti land on us. We never know which descendant will inherit autosomal DNA from which ancestor or in what amount. And much like confetti tossed into the air, the descendants closer to the ancestor generally will have a larger quantity of confetti land on him.