Now new technology reflects those back at you, and lets you peek into the future.
Jon Melko has some good habits.
"I'm very active. If I'm not working, I'm usually in the water diving, swimming, or fishing," he said.
But he has some bad habits, too.
"Smoking, occasionally drinking. Social drinker, fast food -- because i'm always on the go."
Knowing that those aren't healthy habits, he wonders what the toll will be on his body a couple years from now if he keeps it up.
Now a special digital device may have his answer
"Rather than simply provide reflection, what it does is make a transformation on the image and show it back to the person. And, that transformation is intended to approximate what somebody might look like if somebody continues to engage in a prolonged set of behaviors," said Andrew Fano, Accenture Labs.
It's called a persuasive mirror. Under development by Accenture Labs, the hope is people will be able to see how they'll look in the future, and maybe change behaviors because of it.
"A picture is worth a thousand warnings," Fano said.
Here's how it works: you answer a list of questions about your habits, from exercise to how much TV you watch, whether you smoke, and what you eat. All that info is input into a special software program, which then matches it to pictures taken by digital cameras connected to the mirror.
"What we do to make the mirror aspect of this work is interpolate an intermediate image. And, it's on this intermediate image that we apply a series of transformations that are intended to show the effect of certain behaviors," Fano said.
But this is no toy. The lab sees this mirror as a tool for health providers in the future.
Researchers at U.C. San Diego recently put it to the test.
They just completed a study to see how persuasive the mirror might be in the fight against childhood obesity.
"This is a common problem that needs a new way of thinking about it," said health researcher Jeannie Huang.
The mirror can work on any age group and on various behaviors. The concept can be very convincing.
As for Jon, he says it might work.
The results of the study done at UCSD won't be out until May. Then, they'll take that information and continue to fine tune the mirror before they are able to take it to the rest of medical community.