It comes down to the utility of money, or roughly speaking, how happy the money will make you. $20,000 is a lot more valuable to someone with $10,000 than someone with $50,000. In other words, having $10,000 is worth, say, 10 utility, having $30,000 is worth 20 utility, and having $50,000 is worth 25 utility.
Starting with $30,000, buying insurance which has a small chance of saving you $20,000 gives you a +10 utility gain if it pays off. Buying a lottery ticket which has an equal chance of giving you $20,000 gives you a +5 utility gain if it pays off.
Starting with $30,000, buying insurance which has a small chance of saving you $20,000 gives you a +10 utility gain if it pays off. Buying a lottery ticket which has an equal chance of giving you $20,000 gives you a +5 utility gain if it pays off.