system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 If no one knows about your dirty money why do you need to launder it

I know money from drugs, robberies, stolen goods, etc is “dirty” but, how does anyone know it’s dirty? Why can’t you just spend your money?
gpt
People, particularly tax authorities, start to get suspicious when you somehow start spending many times the amount of money that you make. 

Basically, if the money is dirty, it can't really be used for large purchases because the mere fact that you possess that much unexplained cash would raise suspicion of you.