Staying happy in whatever occurs takes discipline, generosity, patience, concentration, perseverance and, most important of all, insight into consciousness. These are called the six perfections (or paramitas, in Sanskrit). Personally, I see these as discipline or training or inner instructions to detach oneself from habitual responses and stay open, and happy.
Smiling kindly is not just an act. It is an expression of intelligence, of inner knowledge, of confidence in compassionate aspiration, and is the wisdom of realisation that all sentient beings have a good heart at their essence.
This doesn’t mean that we go along with either sentimental or evil mentality, but we allow the openness of a spacious mind just to rest in purity, so that actions and reactions exhaust themselves.
We are talking about our own gossiping mind. When we gain more strength, we can incorporate the sentimentality and evil of others. Staying happy is remembering that we are already happy.