Popular TV trainers communicate the idea telling people they suck is motivating.
They are often seen on the look out for diet or exercise deviation, ready to pounce with a heavy dose of 'tough love.'
In real life this shaming never works. Such extreme and cartoonish behavior as that which can be seen on shows like The Biggest Loser can be described as 'What's bad coaching.' They are always looking for the bad, not the good.
I've seen this mentality practiced throughout my time in the fitness industry. I hate to admit I've participated as well.
"Your gluteus aren't working. Fix it with this exercise."
"Your food is wonky. Fix it with this menu."
"You're missing these nutrients. Fix it by trying this supplement."
No matter how I dressed up the language the pattern was the same: identify a problem and provide a solution to fix it.
This presents a few issues.
One, just because someone needs help with their fitness and nutrition that doesn't mean they are all broken. Actually, the people who hire coaches are typically high performers elsewhere in their lives. For every client I coached how to eat properly or move correctly there are just as many who could coach me on how to run a business or family. Areas where they are an expert, not met. So people who have coaches aren't broken. Far from it, they are high achievers.
Secondly, no one likes to be made to feel like a screw up. Focusing on the bad over good is a sure recipe for demoralization.
And lastly, coaching with a glass half empty model leads us to feel like we will never be good enough. We may indeed make progress or add a little liquid to our glass but the assumption of always needing more stays. How discouraging. If we are so screwed up as to always be wanting more in our fitness and nutrition pursuits that we will never make progress, are doomed to be 'half empty' and give up trying.
These reasons combined tell us why focusing on what's good is better than focusing on what's bad. It's the equivalent of looking at the glass half full instead of half empty.
It's in asking "what am I good at?" instead of dwelling and trying to constantly fix "what I'm bad at."