Early in his career as Green Lantern, Hal Jordan learned VERY quickly that he had to be very, very specific when giving his power ring instructions. For example, take a look at his fight with Doctor Light in Green Lantern #33 (1964). Back then, Doctor Light was a force to be reckoned with, and in this case was out to eliminate all members of the Justice League, one at a time.
In his fight with Green Lantern, Doctor Light causes all sorts of trouble, including this rather embarrassing situation:
(Sorry -- I always get a chuckle out of that panel.)
Doctor Light then succeeds in knocking poor Hal unconscious and dropping him head-first off a building:
Now, prior to this fight, Hal had given his ring a very simple instruction. That instruction was, to NOT let Hal hit the ground if he lost consciousness.
So Hal's been knocked out, and with the open-ended instruction it's been given, does the ring generate a net to catch Hal? Or even a giant catcher's mitt, to fit in with Hal's love of baseball? Oh, HECK, no. The ring chooses to do THIS:
Well, the air around Hal starts to get pretty darned hot, and he wakes up. Imagine his surprise to find out that he's plummeting through a big, deep hole toward the center of the Earth!
Hal flies back up and out of the hole, closes it up, and goes after Doctor Light. Of course, Hal succeeds in stopping the bad guy, but you can bet he's VERY careful to give his ring VERY specific instructions from here on out.
Stupid power ring.