There's a lot of interesting conflations of "right" versus "wrong" in this this thread. There's the C# "best practices" "right" versus "wrong" of knowing when to choose things like StringBuilder over string.Concat or string's + operator overloading (which does just call string.Concat under the hood). There's the "does that right/wrong" apply to other languages question? (The answer is far more complex than just "right" and "wrong".) There's the VM guarantees of .NET CLR's hard line "no string is mutable" setting a somewhat hard "right" versus "wrong" and other language's VMs/interpreters not needing to make such guarantees to themselves or to others. None of these are really ever "right" versus "wrong", almost all of them are trade-offs described as "best practices" and we take the word "best" too strongly especially when we don't know/examine/explore the trade-off context it originated from (and sometimes wrongly assuming that "best" means "universally the best").