What concepts in the real world can be described by adjunctions?

For example, parents and children are adjoint to one another. Specifically, work in $ZFC$ plus a finite class of atoms $\mathscr{X}$ (one for each person) and let $${\sf Par}:\mathcal{P}(\mathscr{X})\to\mathcal{P}(\mathscr{X})$$ $${\sf Chi}:\mathcal{P}(\mathscr{X})\to\mathcal{P}(\mathscr{X})$$ the functions sending a collection of atoms to the collection of all the atoms corresponding to their parents or children, respectively. Then $${\sf Par\dashv Chi}$$ since we have a (covariant) Galois connection between the poset $\big(\mathcal{P}(\mathscr{X}),\subseteq\big)$ and itself given by the above functions (your parent's children includes you and your children's parents also includes you*), and a covariant Galois connection is an adjunction. What are some other examples?

*Technically, those of us without children (myself currently included) form a hole in the argument as it stands -- we get sent to the empty set by ${\sf Chi}$, then back to the empty set by ${\sf Par}$ again instead of a set of people containing ourselves. To fix this, add an additional atom ${\sf f}$ to the theory called *free time*, and let $\mathcal{L}$ be a relation called *having a life* which is the reflexive transitive symmetric closure of the relation on $\mathcal{P}(\mathscr{X})\cup\{{\sf f}\}$ associating all atoms corresponding to people without children to ${\sf f}$. Now define $$\widehat{{\sf Par}}:\mathcal{P}(\mathscr{X})\to\mathcal{P}(\mathscr{X})\cup\{{\sf f}\}\big/\mathcal{Life}$$ $$\widehat{{\sf Chi}}:\mathcal{P}(\mathscr{X})\cup\{{\sf f}\}\big/\mathcal{Life}\to\mathcal{P}(\mathscr{X})$$ as before except have $\widehat{\sf Par}$ send the empty set to $[{\sf f}]$ and $\widehat{\sf Chi}$ send $[{\sf f}]$ to the empty set. Now, we genuinely have that $$\widehat{\sf Par}\dashv\widehat{\sf Chi}.$$ (All of this is well intended humor; my wife and I look forward to joining the ranks of parents with no free time.)