When designing this experiment, we were pretty sure that cooperation would break down altogether based on what people had previously tried. That it didn't and resembles more what we see in the real world (things generally work and people don't stab each other in the back) was not obvious.

A general challenge in doing social science research is that once you present a new result, someone will always claim that it was obvious because of X. What they don't see was that there was a Y that could have plausibly explained an entirely different result. Once we've shown which of X or Y is more likely, the world updates, but it was not obvious to begin with.

My collaborator Duncan Watts (one of the pioneers in the field of network science) has written a book about this phenomenon: Everything is Obvious, Once You Know the Answer.

Realize that saying something is "obvious" is often not the case, though by definition resilience adds stability and in a dynamic system any addition of any truly resilient element is amplifier of stability, especially in a finite system.

If you're saying that the resilient players might switch to being non-resilient, sure, it's not obvious what would happen, but my assumption is that a resilient player is resilient.

It was not obvious that resilient cooperative players even existed before we conducted this experiment.

Now it's obvious, because we run into nice, prosocial people and of course they fit the profile.

It's not obvious until you prove it, I'll buy that since I wasn't able to win this argument, a few decades ago. I remember being in Philosophy class trying to argue (decades ago now) that tit-for-tat tests were too narrow (too short) and that lagged-strategies (as I then called them) should work better than tit-for-tat in longer trials. The problem I saw with tit-for-tat being that you can get mutually locked into it; it's very common in real life to have two players/friends/spouses thinking the other began a barrage of mutual retaliation first. So incorporating at least brief resets or periods of forgiveness seemed a better strategy to me. An example of this lock-in from real life is that people who (often do to an abusive childhood) commonly misread others actions as deliberately hurtful to them end up divorced, or not able to get to marriage in the first place, often after a ton of tit-for-tat fights they think their partner started. Ditto, those who don't spend a lot of time thinking about the consequences for others of their actions or whether those could be misinterpreted.

Anyway, I made no headway with my professors (or other students, probably.) They were happy to call the results they then had proof that tit-for-tat was tops, and always would be 'cause it was such a simple, logical strategy. So, no, I can personally assure anyone who cares to know that it wasn't obvious to the experts then. As for laypeople... well it's most accurate to say they had no opinion; it was rough trying to explain PDs back then since they violated everyone's "folk expectations" in some way, whether you were religious or a rationalist and were rarely spoken or written of outside of academia.

I'd also say I didn't know it then, either; I just suspected - since it wasn't perfectly clear that my analogy from more ambiguous real-life exchanges would hold in such clearly-defined circumstances.