The line spacing of a paragraph is done, when TeX breaks the paragraph into lines. This happens at the end of the paragraph.

In the case of the question, environment explain uses \setstretch{0.1} and \footnotesize. At the end of the environment, the paragraph has not yet ended, but the environment does. Therefore the local settings of the environment are lost and the paragraph end by the next empty line uses the settings that are active after (= before, = outside) the environment. 

As Barbara Beeton said in her comment, \par in the end part helps (if it is ok, if the environment ends the paragraph).

\newenvironment{explain}{%
  \par
  \medskip
  ... \footnotesize
}{%
  \par
}


more fun with inside-table spacing --- setspace
I would like to remove one of the outlets from a circuit, and run a dedicated wire to it from a separate breaker, placing it on it's own circuit.

When I disconnect the existing circuit from the receptical, that will leave pigtails for the old circuit.

What do I do with the pigtails from the old circuit that the outlet will no longer be wired to?  

-Do they need to stay in the box(which would mean they would be pigtailed in the box, but not connected to the outlet, and new wiring would also run into the box for the new circuit connected to the outlet)?

-Get pushed into the wall?

-What seems the safest thing: Remove the outlet, leave the pigtails in the box, and put a blank over it. Then cut a new hole for a new box for the receptacle and new wiring to go into.
