Sometimes the smallest thing can make a huge difference. Take for example the mouse. You may have an iMac with a Retina display, but the keyboard and mouse are still the same design as when the aluminium iMac was introduced — i.e. not very comfortable, nor friendly for your carpal tunnel (your wrist). Replacing the keyboard by something better is not going to be simple, but replacing the mouse is easy: just buy something that makes you control the cursor as if you were holding a pencil, because that’s your hand’s most natural position.