When we work on our own personal projects, we espouse the ideals of the agile manifesto:
Individuals and interactions over processes and tools
Processes go right out the window when you're working on a project by yourself. There's no need to do sprint planning or other team ceremonies. Code doesn't need to go through a UAT because you're testing things as you go along.
Working software over comprehensive documentation
Has anyone documented their own personal projects? Documentation isn't important when the number of communication paths is zero. A lone coder on a project only cares about working software.
Customer collaboration over contract negotiations
Collaboration with yourself - because you are the customer - is perfect. Whatever you dream up will get implemented.
Responding to change over following a plan
There is beauty to the flexibility a single software engineer has over a project that only interests them. There's no heavy-handed planning needed, and new ideas can be implemented whenever the engineer desires. Feature prioritization is instantaneous.
Therefore, personal projects are the pinnacle of the agile methodology.