Leading with positivity, optimism, love, and joy are a super important part of living a full, meaningful life. However, we are human, designed to experience a full range of emotions. It can even be harmful to our mental health and overall wellbeing to only express positive emotions.
I've spent a lot of time learning how to express my full range of genuine emotions. Smacking a smile on my face came very easy for me, but emotions like anger, sadness, frustration, disappointment, etc... were more difficult. I was the type to say "yes" to too much and bottle it all up until I was about to explode. I'm still a work in progress, but let's just say, a mindfulness practice is VERY worth the time (and the financial investment too)!