What’s the reason behind burn out of CFL?
I used it for just 4 months and it burned out.
Why so? due to high voltage or something?? or any other reason

There can be many reasons for this to occur. Most likely its just a defective bulb. I have had these from time to time and simply returned it to the store with receipt and got another one. These bulbs when purchased typically come with a warranty, but you must retain the paperwork that comes with bulb to get this.

Well, I think that might have happened due to high voltage.
Sometimes, in some cases that just happens due to high voltages and can be same in your case i think.

With power delivery systems now a days it is very rare to have a voltage spike high enough to burn out a bulb. Had you recived such a spike a lot more then just one bulb would have been ruined. I am sure its just a defective bulb in your case.

I don't have HCC's faith in our nation's power delivery system. Having lived out in the country most of my life, it is quite common to go for months without having to replace a bulb, then have a half dozen blow in a week. I don't know what kind of voltage spike or power fluctuation it takes to burn out an otherwise good bulb, but I'll keep blaming a lot of it on the power company.

Since most of our bulbs, fixtures, wiring, and connectors are now manufactured in 3rd world countries, though, to keep the prices where we like them, we see a lot of variation in quality, so along with the power company I will place shared blame on both the Chinese and on Walmart!

Think your bulbs are burning out fast now. Wait Our new pres is attempting to pass a bill that will require all light bulbs be high efficency to save the planet from climate change.
All a crock of you know what. But in the end it will all cost us big bucks to convert our lighting.