I thought there was a difference between those two in how they start burning, like one needs an external flame to start while the other can burst into flame without an obvious ignition source.
Perhaps perhaps.
But what joyful means to you likely differs from what it means to me, simply because we haven’t read the exact same literature and had the same conversations.
True true.
Happy: Joyful, cheerful, merry, delighted
Or
Beautiful: Lovely, pretty, attractive
The only truly identical synonym I can think of is flammable and inflammable