What's with the word "pickle" being associated with a troublesome predicament?

The phrase has to do with the actual pickling process, where the pickles are sealed in a brine solution...the inference is that there's no easy way out.
It has no relation to the qualities of the pickles themselves
The earliest known reference to being "in a pickle" appears in a Shakespeare play.

They're good but I don't think I would want to be inside one

Pickles are the nice guys of cucumbers