Never forget to look at the big picture
Here is a little thought experiment: you have spent 100 euro on a concert ticket. Standing in front of the concert hall, you are patting your pockets with a long face – you have lost your ticket. You could spend another 100 euro on a new ticket. Will you, though?
Another scenario: you have deposited the concert ticket at the box office. When you reach for your wallet to pay for it, you notice that you have lost it, including the 100 euro for the ticket. Luckily, you find a 100-euro bill in your jacket. Will you use the money to buy the ticket?