Use either as appropriate. THIS ...f you are discussing a specific subject, thing, idea, etc. IT if you are discussing a specific subject, thing, idea, etc. English is a very flexible language. Do not be so quick to presume that some kind of rule prohibits flexible usage. It is a nice day. This is a nice day. It is a nice coat. This is a nice coat. It is a love story for the ages. This is a love story for the ages. It is a disaster. This is a disaster. It is true that I love you. I love you; this is true. This is not the right way to the airport. It is not the right way to the airport. It is exactly what I would do. This is exactly what I would do. It is yours. This is yours. (Hope that helps.)