Shawn Achor, an expert in positive psychology, argues that the notion of happiness coming after success has things the wrong way around.
He argues that with success - as we approach our goal, we quite naturally and reasonably, redefine success and move the goal posts further away (eg, I've got a job, now I want a better job, I'm exercising regularly, now I want to run a 1:30 half marathon). If happiness depends on our definition of success, then we never quite reach happiness, as Shawn puts it 'happiness is beyond the cognitive horizon'.
Rather than seeing happiness as something that is determined by external circumstances, Shawn argues that happiness is something that you train your mind to do, regardless of your circumstances.
He argues that once you are happy, you will then be more productive.
Some suggestions he has for training your mind to be happy:
Three gratitudes - Once a day, write down three things that you are grateful for.
Journaling - Five minutes a day, write down something positive that has happened that day.
Random acts of kindness - Once a day, email people in your professional and social circles acknowledging something good they've done.
The argument is, that by practising these things, your brain gets in the pattern of recognising good things.
This produces optimism - believing that your actions do matter, and this helps with productivity - knowing that the work you are doing now, is going to have a real result.
Here a couple of videos by Shawn Achor: