How do we value, gain and loss?

What is gain, and what is loss? When we gain, what do we gain exactly? Do we not loose something, when we gain something? Are we aware of all our gains, and all our losses? When we make a purchase, there is a gain of goods, and a loss of currency. We gain, instantly, as we loose, in a transaction. Are all gain's and losses of the same nature? If we make a gain now, the consequence of which will make us loose at a later date, then can the gain and loss, not be seen as a simultaneous happening? Is a financial transaction, the most visible example of the process of gain and loss?