Even better would be: "It's certain that life..."Hello jiaruchan, I'm not a teacher, but I hope my advice helps!
I believe "assured" is a better word to use in that context.
It is an assured thing that life would be very hard without electricity.
Do we have a sentence pattern like:
It is for sure that life would be very hard without electricity.
It is for sure that...=It is a sure thing that....?