Happiness and suffering are states of mind and so their main causes are not to be found outside the mind. If we want to be truly happy and free from suffering, we must learn to control our mind.
Through practicing Buddha's teachings we can develop and maintain a peaceful mind all the time, so that we will be happy all the time; regardless of whether our external conditions are good or bad. We can test this through our own experience.
Buddha's teachings allow us to maintain a good heart and a loving mind towards everyone - regardless of their background, appearance or behaviour, so we can become the best version of ourself.