Just a few reasons:

• Because it reminds you of the positive things in your life. It makes you happy about the people in your life, whether they’re loved ones or just a stranger you met who was kind to you in some ways.
• Because it turns bad things into good things. Having problems at work? Be grateful you have work. Be grateful you have challenges, and that life isn’t boring. Be grateful that you can learn from these challenges. Be thankful they make you a stronger person.
• Because it reminds you of what’s important. It’s hard to complain about the little things when you give thanks that your children are alive and healthy. It’s hard to get stressed out over paying bills when you are grateful there is a roof over your head.
• Because it reminds you to thank others. I’ll talk about this more below, but the simple act of saying “thank you” to someone can make a big difference in that person’s life. Calling them, emailing them, stopping by to say thank you … just taking that minute out of your life to tell them why you are grateful toward them is important to them. People like being appreciated for who they are and what they do. It costs you little, but makes someone else happy. And making someone else happy will make you happy.

Source:  www.zenhabits.net