Why Smartphones dead / brick? all about brick !

what is Brick ?

Bricking means Device is not in function or the only function left is to use it as paperweight.

Why Smartphones dead?
  Behind bricking your device there could be a numerous reason but generally it happens due to

1) Misconfiguration in the system files.

2) Wrongly flashing files of another device.
3) Error in the flashing file or improper or corrupt download.
4) Malware can also be the cause.
5) Interupption between the update process.
6) Flashing recovery files from flashing tools or vice-versa.

Types of  Brick
There are two types of brick
1) Soft brick
2) Hard brick

What is Soft Brick ?

      Well soft brick is a state where bootloader fails to load the android system files due to the reason mentioned above and it actually shows the sign of life like rebooting again and again, stuck at boot screen, etc. Bootloader is a program which stores the booting sequence and runs first and then loads up the android system as a sequence part.
     Soft brick can be recovered easily as it just requires corrupt files which needs to be replaced with the fresh files. Flashing entire ROM again helps to get over with this issue.
    There's lots of guides are available to recover the device from the soft bricked state.

What is Hard Brick ?

     Hard brick is a state where bootloader does'nt know how to boot up i.e bootloader files are corrupted or booting sequence is messed up. The device is not showing any sign of life like power key is not waking up the device. It is generally due to flashing wrong files or another device files or recovery files not from recovery but from tools like odin, fastboot, etc. Tools flashing softwares comes with various options and generally flashables files comes with whole package with bootloader files inside and if anything goes wrong and bootloader is wiped or wrongly flashed the device is dead.
      Recovering device from Hard brick state is very less. A normal user cant do cuz it requires to write boot files again and this is done by JTAG but chances are very less so ultimately motherboard change in the only way.

Chances of bricking ?

1. Well soft brick is normal as it happens to all of us and chances of soft bricking of phone is 70 to 80 percent cuz lot of times it happens cuz some files of previous roms are still present in the system and bootloader is getting confused whether to load old file or new file. Making a full wipe and installing rom again always solves the problems. Flashing the entire rom is also a way to start fresh and get over with soft brick issue.   
2. Hard brick is very rare and if you follow the guides there will be 1% chance of Hard bricking your device. Unless you made a mistake.

So, it is always advisable to do the following :

1.  Always follow the guide from trusted sources like this forum for Mi devices and XDA for all other devices.
2. Always check if downloaded files are corrupted like checking if zip files are opening or comparing size of files displayed on the site with that of downloaded one.
3. Always charge phone to 70% atleast to avoid interupption of running out of juice.