A loan is money taken out from the future. You borrow a certain sum today to pay it back with interest tomorrow.
An investment is money lent to the future. You invest money today so that it pays dividends tomorrow.
Some behaviours are akin to borrowing from the future. A night outside with plenty of alcohol makes you feel great, but is repaid with interest in the future. To drink is to borrow happiness from tomorrow.
Some others are akin to investing in the future. Going for a run in the cold feels downright unpleasant. A few years from now, it pays dividends with better health and an increased lifespan.
When you engage in a certain behaviour, are you taking out a loan or making an investment?