A friend of ours shared the eulogy he gave for his dad. In it, he quoted a lesson his father taught him as a kid:

Watch your thoughts, they become words;
watch your words, they become actions;
watch your actions, they become habits;
watch your habits, they become character;
watch your character, for it becomes your destiny.

(This quote and ones with a similar sentiment are often attributed to many different sources. Ultimately, the original is by Frank Outlaw based on Quote Investigator's research.)

I don't think I was taught to watch my thoughts as a kid. At least not in a way that was effective for me.

I was taught that particular actions are bad and why they are bad.

I was taught that jealousy, intolerance, hate, etc are bad.

But I didn't realize that the way I choose to think about things can have a big impact on long-term happiness and fulfillment in life. On friendships and relationships too.

I realized in adulthood that being happy is a choice much of the time. A choice made every day. Focusing on the positive (and even helping to amplify it) can do a lot to diminish the negative: disappointment, annoyance, frustration, misfortune.

Of course, really bad things happen sometimes and you can't just ignore them. It wouldn't be healthy to try to force yourself to be happy when you're truly hurting. But for all the small bad things, with practice it's possible to decide how much energy to spend thinking about them -- and whether to think about them at all. Sometimes negativity can be self-fulfilling: expecting to have a bad time can lead to having a bad time.

This is similar to what I'm trying to say in Day and Night. Thinking envious thoughts leads to envious actions. Comparing yourself to others leads to unempathetic behaviors. And envious actions, unempathetic behaviors lead to a lonely life.

On the other hand, looking for the good and trying to be truly empathetic can lead to happiness, more positivity, and supportive friendships.