I've linked to this blog from time to time because I think Justin Bourne does a great breakdown on some of the finer points of defensive responsibility in hockey. Things that happen so fast they're often easy to miss watching realtime.
He shows that it's usually not just because of the goalie or last D-man that the other team scored a goal. It often involves multiple breakdowns earlier in the play.
Anyway, this one breaks down a couple Wings goals against the Senators, and basically mocks the Senators because they all started by making a line change when they shouldn't have.
The Ottawa Senators gave up three even-strength goals to the Detroit Red Wings (as well as an empty-netter to Daniel Alfredsson in his return), and each one of those three can be traced back to the exact same issue: line changes. Yes, in an NHL game. Multiple times.
The second goal nicely highlights a bad turnover by Karlsson followed by Tatar pulling a nice drag move on Karlsson, who makes a half-assed effort at defense.