What actually happens under the hood when a base class lacks a virtual destructor:

class Base {
public:
    ~Base() { std::cout << "~Base\n"; }
};
class Derived : public Base {
    std::vector<int> m_buffer;
public:
    ~Derived() { std::cout << "~Derived\n"; }
};

Base* p = new Derived();
delete p; // UNDEFINED BEHAVIOR!

Because ~Base() is non-virtual, the compiler performs static dispatch calling only Base::~Base(). The Derived destructor is never executed, leaking m_buffer's dynamic heap memory!

The ISO C++ standard explicitly states that deleting a derived object through a pointer to a base class with a non-virtual destructor results in undefined behavior (UB).

Guideline from C++ Core Guidelines: A base class destructor must be either public and virtual, or protected and non-virtual.