Mariana Trench fish "how they can thrive under that extreme water pressure is still a mystery"

New Mariana Trench species is the deepest-dwelling fish in the ocean

Exactly how they can thrive under that extreme water pressure is still a mystery for now, but these creatures have been sighted regularly at depths of around 26,200 ft (8,000 m) and down to a record-breaking depth of 26,830 ft (8,178 m), as captured on video by Japanese researchers earlier this year.

I often see comments like this, but I have not seen any explanation why extreme water pressure would be a problem. Is there a reason?