Why quantum needs fault tolerant?

Hi, I heard about fault tolerant for QC. Can you help me know why?

Hello! If applicable, put your complete code example down below. Make sure that your code:

  • is 100% self-contained — someone can copy-paste exactly what is here and run it to
    reproduce the behaviour you are observing
  • includes comments
# Put code here

If you want help with diagnosing an error, please put the full error message below:

# Put full error message here

And, finally, make sure to include the versions of your packages. Specifically, show us the output of qml.about().