and so
That's because we've now assumed an inconsistency, and from it we can prove anything, no matter how ridiculous:
\[P \land P' \longrightarrow Q\] If we forget that we are mortal, and operate under the assumption that we are not mortal, then all hell will break loose.
If we operate under the assumption that we are not mortal, then all hell will break loose.
We don't need forgetfulness; forgetfulness is not necessary; operating under false assumptions is sufficient.