What are potential pitfalls of using variables without checking their existence in PHP scripts, and how can these errors be prevented or resolved?

Using variables without checking their existence in PHP scripts can lead to "Undefined variable" errors, which can cause unexpected behavior or even security vulnerabilities in your code. To prevent these errors, you should always check if a variable is set before using it, either with `isset()` or `empty()` functions.

// Check if the variable is set before using it
if(isset($variable)){
    // Use the variable here
    echo $variable;
} else {
    // Handle the case when the variable is not set
    echo "Variable is not set";
}