Seen from a distance, life is a cycle: birth, reproduction, death. The next ones repeat the process. Obviously, when analyzed in details, things get much trickier, but even without stepping into this kind of complexity, the symbolism of the circle and the associated geometry is interesting.
While the wheel is an ancient "invention", I like how this basic geometry shape embeds a notion of infinity: even if you know the diameter, you cannot express the exact length of the circumference with numbers (since it involves the constant Pi, which decimal representation never ends and never settles into a permanently repeating pattern). Simple at first glance, full of endless surprises in fact!