The act of buying is a conversion from a symbolic representation of value (money) into something that matters to you personally. Minimalist philosophy is not against doing that, but against buying without conscious reflection.
In the beginning you begin to wonder whether your stuff is really worth its price to you. Maybe you find out that you don't have the time to actually use it or all of it. Then you start decluttering and downsizing your belongings. Or perhaps you discover that how other people think great deal of something tricked you into believing you need it, too. Hence you pay closer attention to your own true desires the next time you long to have something.
Minimalism is no doctrine that tells you do think before you add something to your shopping cart. It is a consequence of following certain principles. Minimalist living is only a name that describes what happened. Don't look at it as a lifestyle to follow because it has been in the media or someone told you about it. Let it happen from the inside out.