The phrase "banana skin" is an idiomatic expression that means a situation or circumstance that could cause someone to fail, make a mistake, or experience trouble. It refers to something that seems harmless or innocuous but can actually lead to problems if not handled carefully. The origin of the phrase comes from the idea that walking on a banana peel can be dangerous and cause one to slip or fall. In other words, it's a metaphor for something that appears safe or benign but has hidden dangers or risks.