This question is inspired by Why are interstellar colonists lone rangers?. I know that many of its answers are also suitable for this questions. However, I am more interested in ideas that work with harder goals and without extremely-far future technology.
The year is 21XX, and humans are sending their first manned spaceships to venture out of the Sol system. They are several (I would say <100) sleeper ships sent toward different star systems to explore and colonize them. The journey would take several hundred years for the ships, while the human onboard sleeping for most of it. Each ship carries one and only one human on board.
- Why carry any human at all?
- Why carry only one human, instead of a small team or even more?
You are free to define the story background to match your reasoning, as long as it roughly follows this:
Humans have colonized some parts of the Sol system (so they could construct these ships from space). Exactly how much or how little depends on you.
The target star systems are already analyzed from within the Sol system, e.g. with various telescopes, and can even be imaged using solar gravitational lens. However, no probes have been there (except for Breakthrough Starshot, if you really need that).
No FTL technology of any kind have been developed, nor to be developed in the foreseeable future.
Fusion drives are available, but they are nowhere near interstellar torch drives. For example, to get 10% c delta-v, you would need a mass ratio of about 10 (91% of your ship is fusion fuel), and run it continuously for several years.
There can be advanced AI technology somewhere around AGI level. The exact settings depend on you.
The sleeper ships can protect the crew throughout the journey from radiation and other space hazard. The crew will not age when sleeping.
The ships will carry enough necessary machines, tools and resources for the crew to explore and colonize the target star system, which may include some far-future style technology (otherwise the story won't work). Assume that any amount of humans (including zero) would complete the job, although less human would mean more time and less output.
The human on board is not sent away because of a punishment of any kind (or at least he/she does not see it as such), and has received proper training before leaving.
Like the original question, I already have some answers in my head, although they are not very solid. I will rate on how much they would force the formation of a one-man man team, since that's the core of the plot.