Gratitude the is the Difference between Happiness & Misery

I just read an interesting article about a guy who owned a successful restaurant for 12 years. He was asked if he still enjoyed it to which he replied " the last two I have, but for the first 10 years I hated it".
He went on to explain that after the initial excitement of opening had died down, he began to feel trapped, tied down and bored with the same routine every day, the same faces, the same stories and conversations, day in day out.

Somewhere after the 10th birthday of his business, he realized that many small business's like his do not survive that long, and that he should be more grateful that he had such loyal customers, all be it a result of his hard work and dedication despite how he felt. So he began to enjoy how his customers involved him in their life, how his business had allowed him to develop his passion for food.

His new attitude quickly spilled over to his staff and his customers began to bring more of their friends, he found confidence in his staff to be able to take time off and enjoy life a lot more.

What actually changed was that he adopted an attitude of gratitude, which changed his life from misery to happiness and abundance, which then reflected in his business. Nothing external changed, just his mindset.