Think about the last thing you spent money on. It could be anything. Coffee. A book. Movie tickets.
Each of these has a monetary value attached to them. Coffee may seem insignificant for $3 or $5, but try replacing said cost with the time taken to earn that money.
Example: If you make $20 an hour, and that coffee costs $5, it is up to you to decide if it’s worth 15 minutes of work. In a vacuum, probably, but add that up per day (5 workdays a week) and you come to 5 hours a month ($100).
On coffee. Yikes.