A pleasant surprise probably has a greater hedonic impact than being told about the same positive event long in advance - hearing about the positive event is good news in the moment of first hearing, but you don't have the gift actually in hand. Then you have to wait, perhaps for a long time, possibly comparing the expected pleasure of the future to the lesser pleasure of the present. This argues that if you have a choice between a world in which the same pleasant events occur, but in the first world you are told about them long in advance, and in the second world they are kept secret until they occur, you would prefer to live in the second world. The importance of hope is widely appreciated - people who do not expect their lives to improve in the future are less likely to be happy in the present - but the importance of vague hope may be understated.
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