What causes phones to root improperly or brick?

[AC Question]

I want to root my galaxy S4 but I'm more of a windows guy, used to being able to fix any problem no matter how bad it gets as long as the hardware is intact. The idea of creating a problem by doing something I don't understand that is impossible to fix is a bit scary when it comes to my not easy to replace phone.
So before I get into the whole rooting thing can someone tell me what I need to be careful of so I don't break my phone beyond repair.

 

[dpham00]

In general, you need to follow the directions to a tee

 

[SactoKingsFan]

Usually using the wrong root method for specific version of Android, messing up a key step or trying the wrong toolkit. You should read up about rooting the s4 on XDA.

 

[AlphaTango414]

Don't go in blind or with very little understanding about what you are doing. Weigh the pros and cons of non root to root and make sure it's worth the risk. Read, read, read, ask questions, and read some more.

You have taken a great first step in asking this question.