C++ Atomic compare_exchange_weak

Something happened when I used this feature that Was hard for me to understand Code:

    atomic_size_t example;
    example.store(100, memory_order_release);
    //Now example.load() is 100;
    auto result =  example.compare_exchange_weak(1000, 50, memory_order_relaxed) << endl;
    //Now result is zero(false) and example.load() is 100,I knew it would.
    result =  example.compare_exchange_weak(1000, 50, memory_order_relaxed) << endl;
    //But now !!! result is One(true)! and example.load() is 50 Why???

What happens after the function is executed? Why are the two executions different? I can't understand why this happened, so I really hope you can answer my question.Thank u very much.