Not that rare. On a day when it's raining in summer, I can almost always get one if I'm patient and look for the ginormous shadow.
Okay, thank you. It's just I have yet to catch one (in fact, I've never caught one in an Animal Crossing game before), although admittedly my activity up until just a few days ago on New Horizons has been relatively low, since I'll admit that there are various limits to my appeal in the game.
What I've done recently to drum up new interest in the game for me (which I sort of did the same thing with New Leaf given how there were many years in between New Leaf and New Horizons's releases in the West, between 2013 and 2020 obviously, but in New Horizons there are more features to take advantage of in terms of this) is simply to recreate a lot of stuff on my island. With New Horizons, unlike New Leaf, since there are features such as putting furniture outside and terraforming, I simply have more options in that regard. Admittedly (granted, it hasn't been many days though), I haven't done
nearly as much with the terraforming as I've planned and would like to do, but especially with the crafting, I've managed to come up with a lot of furniture items that I like having on my island. I might make some rearrangements with them (which the terraforming would help assist me with), but I'm generally satisfied. It's just a bit, well... hurtful, and makes me feel lazy in terms of my island's quality, when I see some truly
amazing islands on the Dream Suite.
Anyways, how this relates to fishing is that I have a crazy habit of where, whenever I do something I specifically plan to do for my island, I have the impulse to always catch a fish or a bug.

It's like I can't help it. It seems to work to my benefit, though, haha, as I manage to make a lot of Bells doing so, selling these fish and bugs to Timmy and Tommy at Nook's Cranny.