Ooh, a thylacine. I believe it, though. I do think there's some still walking around out there. Or at least were as of a few years ago.
Still, I never kick myself over missed wildlife shots, unless it's on one of those rare occasions I actually have a fairly appropriate lens mounted. (I usually don't.)
I've had occasional chances where it's like, 'Oh, this is beautiful... Long lens is right there... need... more... hands...'
Especially since right now my good long lens for the old Canons is big&heavy at least for me. Bigbig. Non-trivial to carry all day. Thus if it's *right there* and you dont get to bring it to bear... Heheh. A little frustrating. But hard to be too annoyed just cause you saw something beautiful.