damp squib

The phrase "damp squib" refers to something that turns out to be underwhelming, disappointing, or anticlimactic. It originated from the concept of a squib, which is a small firework that fails to explode properly when lit. When a squib gets damp or wet, it becomes even more likely to fizzle out and produce little to no effect, thus "damp squib" is used metaphorically to describe something that fails to meet expectations or falls short of delivering the anticipated impact.