Why do almost all people wait until they get a serious medical problem to then start living healthy?

Hi everybody! Why do almost all people wait until they get a serious medical problem to start living healthy? I'll give you some examples of what I mean in the form of questions. Why does a smoker start stopping to smoke after smoking for 50 years after they find out they got terminal lung cancer, such as emphysema? How come an alcoholic stops drinking after they kill somebody on the road while driving drunk? Why do sexually promiscuous people all of a sudden start living healthy after they get a terrible, incurable STD, like HIV/AIDS? Another example could be why do people deal begin to finally deal with their obesity and being overweight after the doctor tells them they now have heart disease or diabetes? People are weird and procrastinate by nature in my opinion. Any answers would be greatly appreciated! Thanks!

I'm afraid that it's just human nature.
My own mother had lumps on her breast and she knew it, but waited and let it go until she had to have her breast removed. Some people just don't seem to realize or face up to the fact that they are in danger and refuse to see a doctor, example of this is the number of people who look for advise here and for home remedy's. I am not knocking this site, I love it and hope that I and others can help people realize when they need serious medical help.
I go to a doctor when ever I have a problem, rather than wait until it becomes serious. But I also must admit I have been guilty of letting things go.

When people get a serious medical problem that creates an incentive to start living healthy.

Whilst an ounce of prevention is worth a pound of cure most people wait until the pound of cure stage before they start a healthy lifestyle. Whilst people are feeling OK they tend to disregard healthy lifestyles as long as they feel OK. Tomorrow might never come seems to be the motto of a lot of people so they want to enjoy themselves today regardless of the consequences.

I have to believe it is human nature.

On the serious front:
"As I see it, every day you do one of two things: build health or produce disease in yourself."
-Adelle Davis (1904 - 1974)


or on the comedy front:
"Health nuts are going to feel stupid someday, lying in hospitals dying of nothing."
-Redd Foxx (1922 - 1991)