Can I flash another phone's ROM or Kernel on my phone? Can i flash another phone's kernel or ROM on my phone and what would happen is i did so?
Simply put, you would brick your phone.


  But Why? Why if my device is similar to another one. Would it work?


That would also not work because of a for example different CPU, or screen size, etc. 

When building android, you have a device, and a vendor folder. These contain configurations specific to your device, and the vendor folder has what's called proprietary blobs, which are also specific to one device only.

If there is some custom ROM that your device is not compatible with, then if it is open-source, you could have a go at porting that ROM to your device.