G. Alan Marlatt did an experiment to test the effect of alcohol. He divided his subjects into four groups: one group drank a tonic and were told it was tonic, one drank alcohol and were told it was tonic, one drank tonic and were told it was alcohol, and one drank alcohol and were told it was alcohol. The two groups that were told it was alcohol acted more outgoing and flirtatious, regardless of what the drink really was. Those who drank tonic and were told it was tonic had no apparent effects. Those who drank alcohol and were told it was tonic felt sleepy and headachy. So, the effects of alcohol are largely in the mind.
In a less formal experiment, I sometimes buy lottery tickets when the jackpot gets high enough. Right after I buy one I feel really elated and think about how I will spend the money. I won five bucks once, but nothing approaching a jackpot.
Happiness is largely in the mind. The promises of heaven you get from religion are supposed to make you happy regardless of your present circumstances. Most people think you have to achieve something to be happy. But the truth is the happiness comes first. There are many stories about people who won the lottery who suffer tragically in spite of their newfound wealth. You don't know how things are going to turn out. You might as well believe the best is possible.