Do I need to worry about thread safe methods?

[ManiacJoe]

9. This is exactly why you need to think about it.

I still don't understand why there is any concern that a value will overwrite another value, unless the code is sharing a variable among threads.

This is guaranteed to happen since your code is running inside the multi-threaded web server.

Sometimes sharing variables between threads is sometimes a good thing, sometimes a bad thing. Only you as the programmer knows which case your code falls into. If you do not want the variables shared, you need to code in a certain way to prevent it. It is actually quite easy do to; you just need to be aware of how you are coding things.