When you're thinking of making a purchase ask yourself if you would prefer the item of having the money in cash.

Let's say you want to splurge on a GoPro (for the love of god never buy a GoPro) and it will cost $500. Stop and ask yourself if someone offered you a free GoPro or $500 cash which one would you prefer? If you say the cash then don't buy the GoPro and keep your $500. If you decided you would take the GoPro and run then make the purchase.

Now, before you go out and buy the GoPro make yourself wait a week to buy. If in a week you still want the GoPro then go out and buy it. But before you buy it ask yourself can I buy 2 GoPros? If you can't then you can't afford it.

But seriously don't buy a GoPro.