When George and Lennie find the water at the beginning of John Steinbeck's Of Mice and Men, the reactions of the two men are very different.
George is mindful of his surroundings, quick and observant. As the men come into the clearing, Lennie, not doing much more than following, almost runs George over, as if he is not paying attention.
Before George does anything, he takes off his hat and looks around, but Lennie...
...dropped his blankets and flung himself down and drank with long gulps, snorting into the water like a horse.
On the other hand, George is more cautious. He steps nervously to the big man's side to try to stop him:
Lennie!...Lennie, for God' sakes don't drink so much...Lennie. You gonna be sick like you was last night.
George approaches the water cautiously...
I ain't sure it's good water...Looks kinda scummy.
Tastes all right...Don't seem to be running, though. You never oughta drink water when it ain't running.
Lennie falls down and laps the water like "a horse," finally dunking his entire head under—even the unpleasant experience of being ill the evening before does not curb his impulsive behavior.
It is George, always aware of their surroundings, that not only has to warn Lennie to stop, but cautiously tests the water. Even then, George is careful to drink only a little and splash some on his face and neck.
The men's different approaches clearly define their characters. Lennie is impulsive and thoughtless—looking for instant gratification, while George is speculative, cautious and careful. Reading a little further, this process is the nature of the relationship between the two very different men.