A blue-ringed octopus is worth seeing clearly, once, with the glass doing the work your judgment might not. Public aquariums in the countries where these animals live sometimes keep them, and a good exhibit will show you the resting color and, if you are patient or the animal is having a bad moment with a reflection, the rings. You get the size right, which photographs often inflate. You get the slow crawl. You get the sense of an animal that is busy with its own corner and not with the crowd.
The home aquarium is a different proposal. These are venomous, short-lived, particular animals, and the trade in them is one of the pressures conservation writers actually name, alongside habitat damage and the general habit of collecting anything pretty. A private tank also puts a bite within reach of the exact curiosity the public exhibit was designed to satisfy safely. There is no responsible-beginner version of keeping a blue-ringed octopus. The people who work with them do it in institutions, with protocols, and still treat the animal as a serious colleague.
On a shore, the equivalent of the aquarium glass is your decision not to close the distance with your fingers. Binoculars, a camera you do not shove into the den, and a notebook will show you more over a week than a bucket will show you in an afternoon. The bucket ends the observation at the moment it starts, because the animal’s next act is the warning, and the act after that is the one everyone regrets.
If a local aquarium has them, go. Read the label, including the species name if they give one. Then, if you are later standing in a real pool in that animal’s range, you will know what the faint circles mean, and you can have your look from the path.