People always think their ICO will be the next bitcoin before they invest.
Yup. Most are driven by the hype, don't look that the projects, although they have a valid team, either have no usability at all, either "cover" a direction already covered by many other projects, either the project status is not as great as hyped (and may not really advance in the "next" months)... The reality is unveiled after the hype is over.
In some cases there's even a manipulation. Some traders use to buy ICO tokens after the ICO has ended, when the price is not artificially inflated anymore, or it's even lower than the actual worth.
Some big role may also have the inexperienced crypto investors that have no idea how to invest and have no patience at all; they'll see the price drop and they'll panic sell.