Practice being "here and now" during the day.

The more you practice  the easier it is to connect to the activity you are doing and the easier to feel good. 

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And you realise that  the moment you are present,  you can "choose" how to feel.

And come to the conclusion that  "happiness is here and now".

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There are times where you need to think of the past or future and that is fine.

The rest of the time,  "come back to the present"  and feel alive.

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