Only enclosed groups can be killed
Found this proverb at Improve Fast at Go http://users.eniinternet.com/bradleym/Ch1.html Near the end
It sounds like a simple truth but still how often do you try to kill a group that can connect to another group? Or worry about eyes while you can connect to another group?
Also the idea is:
To the extent feasible -- Avoid Becoming Enclosed
To counter an enclosure threat --"If In Doubt, Run Out."
Because only enclosed groups can be killed,-- There Is Little Value In Playing “Inside” Moves Against An Unenclosed Group.
and also
It’s usually better to play outside moves, and force your opponent to make eyes and "live Small"
Caution
These principles are not absolute! There are circumstances in which the global position makes it more advisable to strike first at the opponent’s key shape point(s) to prevent an easy two eyes, and then profitably harass the fleeing group as it struggles to either connect or secure its eyes in the center.
A good read. The publication also gives examples. Improve Fast at Go http://users.eniinternet.com/bradleym/Ch1.html
Everyone makes a big fuss about Lessons in the Fundamentals of Go, but IMHO, "improve fast in go" is far superior in actualy teaching you fundamentals. Also a much easier read. LuisSousa?