I don't know that it isn't real, at least not with absolute certainty. What the eye roll likely signifies is some combination of the following:
- Mild disappointment in response to the realization that you actually believe this stuff,
- Familiarity in the sense that I've been down this road too many times to count and can anticipate where this is likely heading, and
- Bracing myself to be called all sorts of names when I calmly explain why I think you are probably wrong.
How could you possibly have any idea what I have previously investigated? How could you know whether I spent years of my life desperately wanting to share your belief and doing everything in my power to do so? Don't think I'm familiar with the phenomenon in question? Why would you assume that?
Much of the time, the reason I am not investigating the phenomenon or joining you in your belief because I have already looked at the evidence and did not find it remotely sufficient to justify continued effort. I now judge the probability of this thing existing to be so minuscule that it does not appear to be worth my time. I cannot distinguish between a world in which this thing is known not to exist and the present world.
Of course, I remain open to genuinely new evidence of sufficient merit. But really, when substantial new evidence is provided to support the existence of one of these entities, do you really think I'll need to hear about it from you? It would surely be the biggest story of the decade! I'm fairly sure I'll hear about it.