> you can't be trapped in a sub-optimal situation and be rational at the same time

Yes you can that’s what tragedy of the commons is. Rational means you take the choice that provides the most value for yourself. Without a cartel (hard) or government regulation this situation happens all the time.

> Rational means you take the choice that provides the most value for yourself.

provides the most value over what period of time?

making every choice such that each choice, considered in isolation and unto itself, nets you the most value compared to what other choices would've gotten you at that same moment is analogous to best-first search. no one would say that best-first is the rational way to search for a path in a graph, because of all the ways it fails. so my question is, if there's one of those tragedy-of-the-commons situations that happens all the time, why do we insist on saying the participants are acting rationally when they are, metaphorically, walking into a wall forever?

Tragedy of the commons is when a shared resource is rationally used by the individual, but harms the whole.

You can be trapped in sub-optimal situation because it's a local maxima; not because of tragedy of commons, which is something different.

Society can be trapped in local maxima and that would be because of tragedy of commons, and individuals can be trapped in local maxima but that's distinct from tragedy of commons.

Yes and no. It's not a new problem for humans and it's a pretty solvable problem if social pressure and structures can be applied once it is identified. As long as the resource is to be used by a community that depends on it and not an outsider then we are able to keep ourselves mostly in line for the benefit of the group.