How safe is ETF?

How safe is investing in Exchange-Traded Funds (ETFs)? Can they offer stable returns despite market fluctuations? Are ETFs diversified enough to mitigate risks? Do they come with any hidden costs or fees that investors should be aware of? Are ETFs suitable for both long-term and short-term investors? How do ETFs compare to other investment options in terms of safety and performance? Are there any specific ETFs that are considered safer than others? Can ETFs be a reliable source of income for investors? Finally, what are the best practices for investing in ETFs safely?