He is a wise man who does not grieve for what he has not, but rejoices for what he has

You will have some bad days. You will have days where you will do everything right, and still not get the deal, or you will fail a presentation. These days are precious. These days are a gift, despite all the frustration they can bring, because these are the days when you will grow not your skills, but your character. And one of the most important traits of character is to be happy, no matter the circumstances.

Be happy. Be happy because it works. Be happy because if you are not, a lot more things will start going wrong, due to your mood and demeanor. But most importantly, be happy because you always have good reasons to – reasons many tend to overlook, and instead focus on what is cause for grievances.