Fault.

The window?

The guardrail that gave way?

The father who opened the window earlier?

The mother who moved the ottoman too close to the window?

The gate that inexplicably stopped being baby-proof that night?

The nanny who ran into the other room to grab his bottle?

The parents who were away at a colleague's baby shower?

The decision to buy an apartment on the 15th floor?

The gusty winds that day?

The decision to go to the party?

The invite?