As people, we often search for joy in the wrong places.
We fill our lives with activities and people that we think will be our source of joy but...then they fail us and we are left where we were before hand - with an empty joy that's dependent on shifting things and people instead.
We also allow our circumstances as well as people try to steal our joy.
Also, let's be real, our adversary the devil loves to try to steal our joy buy we need to Armor Up daily - in other words allow God's full armor to deflect the arrow the evil one slings at us. (see Ephesians 6:10-18)
It's been well said, like in the brief video above, that... one of the secrets to experiencing joy it to keep seeking God where we doubt He is.