even easier (as weightlifters, powerlifters, bodybuilders all know):

weight comes from your mouth, not from the gym

abs are made in the kitchen

80% diet, 20% training

80% diet, 10% training, 10% sleep is the one I like. A lot of people overlook how important sleep is.

Abs are made in the kitchen, but as someone who went from 22% bodyfat to 11% they are pretty puny abs if you don't pair it with some pretty frequent exercise.

Abs are made in the gym and revealed in the kitchen.

Can't outrun a fork!

While that's true in isolation, if you do the birth control thing of success rate with average usage, I imagine diet alone will massively win out. Diet and exercise, to someone who does not enjoy the exercise, is significantly harder to do than just dieting. People who struggle to lose weight generally struggle to achieve just one of dieting or exercising, so advising them to focus on the easier and more effective option is best.

Obviously, it varies person to person - if someone enjoys a team sport enough to exercise and still combine it with good diet, great. Those people don't tend to be the ones struggling with weight loss, however.