Problem with Boolean modifier-difference I am modelling a PS4 where I need to make a hole in the console that resembles the PS4 logo. I have tried Boolean difference, it works for P and S but not for 4. Knife project also does not seem to work. 

Is it a modelling issue? I am not able to figure it out.
The logo and the console.


How it actually looks like, the P and S are only intersecting the mesh

Blend file
The reason boolean difference fails on the 4 is due to non-manifold geometry. You can select non-manifold geometry with CtrlShiftAltM in edit mode. In your case, this reveals an unconnected face on the extruded version of the 4 (likely due to an extra edge before extruding):



I added an extra edge ring and merged the corresponding faces:



And then the boolean succeeds.