Imagine you are debugging a C++ application where a certain condition seems to always evaluate to true, even when you expect it not to. What could be a common mistake related to relational operators? 

In C++, the single equals (=) is an assignment operator, meaning it assigns a value to a variable. The double equals (==) is a comparison operator, which checks for equality. A common mistake is to use a single equals sign instead of a double equals sign when trying to compare values, leading to unexpected behavior.