If you’ve never had something but wish you did, continuing to wish for it won’t help. If you know you can’t change something, accept that you can’t, you’ll have more peace that way.
If you have something, accept it for what it is and be happy with it. Don’t dwell on the things you can’t change, on the things you don’t have but want and on the things you have, but you wish were different.
Just be okay with things because being okay with things, will serve you better in the longer term.