You and I...we see each other every day.
One day, I say to you "Hi! What colour was the car parked next to you in the parking lot today?"
You would probably give me a weird look and say "Ummm... I don't know, and stop being weird."
Then I see you the next day and I say to you "Hey! What colour was the car parked next to you today?"
Again, you would reply "I don't know! And I told you to stop being weird."
But the next day, you drive up, park, and glance over with intention to check out what colour the car is parked next to you because you know that stupid idiot, me, is going to ask you the same stupid question.
Positivity works the same way.
The more you look for opportunities to see positivity, the less your brain has to work to see it.
And because you've trained your brain to see the positive first, the less likely it will be to fixate on the negative.