Why are my ETFs losing money?

I've been investing in Exchange-Traded Funds (ETFs) for quite some time, but recently, I've noticed a significant decline in their value. Could you help me understand why my ETFs are losing money? Is it due to market fluctuations? Or could it be specific to the ETFs I've chosen? Should I be concerned about this trend, or is it just a temporary setback? Could you provide some insight into what might be causing this loss and what strategies I could adopt to mitigate the risk?