Being 'sure as a pickle' means not being very sure at all. Using this phrase often gives a sense of false hope, as it sounds
like an optimistic phrase while actually being quite pessimistic.
Pickles are very unsure organisms, as shown by their common trait of rolling around on tables. This behavior is caused by the existence of their many bumps, which bother them to no extent. They feel bad for each and every one of these bumps, which they must
lie on and
crush, no matter which way they roll. Thus, they must keep moving.
Nothing is ever less sure than a pickle.
Person 1: So, is our plan
still on for tonight?
Person 2:
Um, probably.
Person 1: You sure?
Person 2: I'm as sure as a pickle!
The next
day...
Person 1: You didn't show up! What happened?
Person 2: I told you, I was as sure as a pickle, which is really not very sure at all.