While being smart can be a necessary condition for making it to the end of your PhD (or, more general, for being successful in life, regardless of what you do), it is not the only important factor. It might not even be the single most important factor.
When working towards a goal, four factors are equally important:
I just said that it is not the only factor that determines the outcome of your undertaking, but it is an important factor nonetheless. And we're talking about intelligence in the broad sense here - not just having a high IQ. We're also considering emotional intelligence, street smarts, wisdom when it comes to making choices in life, and tactic thinking when it comes to making career decisions, or deciding what to spend your time on.
If you take on a large project you want to bring to completion, such as a PhD, then you need to be organized. We've covered time management, managing a research project and more topics on getting organized and being productive on this blog before. Now is the day that we put everything in perspective, and I would like you to realize how all these elements are part of a bigger set of behaviors that increases your chances of positive outcomes.
Don't worry be happy! We're not talking in the sense of going off to the beach and drinking cocktails (although you certainly should do this every now and then, just not continuously), but in the sense of taking life with ease and expecting the best. I've seen good students getting torn under by the quicksand of pessimism. Don't fall prey to this trap, just keep your dreams and hopes high and expect them to be fulfilled sooner or later if you work hard. You'll be a more pleasant person in your family and with your friends if you decide to replace your frown by a smile. Yes, it might be hard in the sour environment of academia, but remember that all that whining and going between eachothers backs has never made anyone's life better. Go for smiles and gratitude instead.
And when the going gets tough, you need to be able to hold on tight and continue the ride. I've been writing about the importance of perseverance before, and that piece ties in with my message of today on how these different elements are interrelated. The gist of the message is that, at times, you will need to roll up your sleeves and clean out your stables. Do it bit by bit, maybe with the help of the pomodoro technique. Think about the bigger picture, and know that this tedious part is a step towards figuring out something pretty cool. Get comfortable in a good chair, with some good music and a nice cuppa tea. Don't start browsing around the internet to procrastinate - you'll feel better if you stay in your office for less hours but finishing more work. And at the end of the day, go do something fun: exercise, good food, reading - reap you reward of a day of hard work.