A hammock needs two posts, often two trees, to hang between. Similarly we need the support of others, even if just two others, to be truly functional. Ecclesiastes 4:12 "Though one may be overpowered, two can defend themselves. A cord of three strands is not quickly broken".
As an aside, this image of a cord with 3 strands is often used to encourage couples in a relationship to include God as their third support.
