Pandora and the son were both curious. Pandora was curious about what was inside the box. The son was curious about how the paw worked.
Since everyone was curious, both of the endings were bad.
In both "Pandora's Box" and "The Monkey's Paw" curiosity ruled. But in "Pandora's Box" Pandora hid the box under her bed to try to stop her curiosity. On the other hand, in "The Monkey's Paw", the characters left the paw out in the open.
In Pandora's box she had to open the box to reveal what was inside and in "The Monkey's Paw" they had to wish for what they wanted.