What is the downside of ETFs?

Could you elaborate on the potential disadvantages of investing in Exchange Traded Funds, or ETFs? I'm particularly interested in understanding the risks associated with their performance, as well as any potential limitations or constraints investors might face when utilizing these financial instruments. Additionally, I'm curious about any fees or costs that might be involved in ETF investing, and how they might impact the overall returns. Could you provide a concise yet comprehensive overview of these downsides?