Maybe you need a realistic Halloween costume, or you are making a feature film for YouTube, or you need a really good excuse to get off work, or whatever. Sometimes you need to be able to create a good fake injury that looks real. You can do a lot with makeup if you know the right techniques. For example, you can...
Create a black eye:
Create a cut:
Another way to create open cuts:
Create a broken nose:
Your fake broken nose will never be able to do this however: Real broken nose