Most houses in the US are surrounded by lawns; and generally the bigger (and thus more expensive) your house, the bigger your lawn. Having a nice house and lawn is a status symbol, and homeowners sometimes/often compete with their neighbors to over who can grow the greenest, lushest, smoothest, best lawn. Of course, this takes hours of work in mowing, fertilizing, weeding, etc. for not much more than a patch of inedible greenery and a transient feeling of mild superiority. The quote is saying that happiness lies in leaving (as in leave alone/leave behind) the lawn and all the time and bother associated with it; and spending that time and care with friends and loved ones.

This is how I understand it: The classic middle-class ambition for retirement is to have your own house and garden, as well as plenty of money in the bank; the symbol of this dream of health, wealth and contentment is a beautiful well-kept lawn. Having a well-kept lawn needs a lot of time and dedication, so it's seen as every man's dream to have both the leisure time and the good health to spend his old age making his garden look perfect. When a stressed, overworked middle-aged person (with a job to go to, bills to pay, and no time for gardening) thinks of retirement, the dream scenario is to be a happy, healthy and relaxed retiree with nothing to worry about and nothing to do all day but cut the grass, water the roses, and then sit in their lovely garden reading the newspaper. At least, that's how the situation is portrayed in stereotypes here. I don't know if it's the same in Spain (or elsewhere), but in the UK you'll see images like this in every health insurance and pension plan advert. The writer of the article is telling us that this is not the key to happiness, though. According to the writer, happiness is not about having money in the bank or a well-tended garden - it's about connections with people. They're telling us to stop watching the stock market (forget the investments) and stop trimming the edges of your flowerbeds (leave the lawn) and call a friend instead.

it’s not a common expression so it’s best to ask the author what they meant by it, lol. I can only speculate that “lawn” represents a territory of wealth that everyone mistakes for true happiness and so badly aspires to. so author says - get off it and go find happiness in simple things.