Sometimes circumstances dictate that you're going to struggle, you're going to hurt, you're going to cry. It is impossible to always be happy. You can experience moments of happiness but they're just for a marked space in time. Emotions & feelings are fleeting moments that can lead you to perceive that something is real when in actuality it is not. Drugs for instance can make you perceive happiness or sex with a stranger can produce that effect. Both of which are negative and yet can produce a feeling of euphoria.
Happiness can be experienced through something positive or negative but we need to take heed to not make decisions based on how we feel. My point is, satan will try, within circumstances that God chooses to allow, to steal, kill or destroy what purpose God has for us. Satan will try you and sometimes we'll feel like we hit rock bottom even if we've managed to follow God to the best of our ability. Even if you lose it all, even if God allows us to be stripped bare, ask yourself if satan was clever enough to do it or was it God that allowed it with a greater purpose in mind?
Joy in the mist of pain, betrayal & tears is a revealing moment to us that far surpasses a feeling. To me, joy reverberates in me the truth of who I serve and who I belong to. It is a knowing deep within my spirit that gives me a peace and comfort that what I have gone through is not the end but the beginning of what my Lord has entrusted to me. So yeah, satan can't steal my joy or happiness or peace or blessings because he's gonna have a heck of a fight on his hands. What God has given me only God can take away and this joy I have He gave it to me freely. No take backs.