The grass is always greener on the other side
It appears that other people’s lives or situations are better than our own
e.g. Alex always envied people who were self-employed but having left a 37hours a week salaried job with a good pension, working for himself 7 days a week with little income, no pension & no security, he remembered that the grass is always greener.
The fuller idiom is “the grass is always greener on the other side of the fence”. It is used - not to support this idea - but to warn of the temptation to think this.