Working smart involves identifying the things you need to do that will give you the best results. The Pareto principle is a perfect example of doing just that. It states that 80% of the effects come from 20% of the causes. The percentages here are not meant to be absolute (although they are strikingly accurate in most cases), but are there to give you a rough estimate in terms of the lopsided differential between the two concepts.
Hard work is great, but it should be applied to the work that’s been “filtered” by working smart FIRST. You work hard after you learn how to work smart and as a result, reap the best benefits of both worlds.