Why did Steinbeck choose the title 'Of Mice and Men'?

Of Mice and Men

Steinbeck originally titled it Something That Happened, however he changed the title after reading Robert Burns' poem, To a Mouse. That poem tells of the regret the narrator feels for having destroyed the home of a mouse while plowing his field. In essence, it suggests that no plan is fool-proof and no one can be completely prepared for the future.
The line from the poem: "To a Mouse" is often translated into English as: "The best-laid plans of mice and men often go awry (or astray)." However, the original Burns Scottish is: "The best laid schemes o' mice an' men / Gang aft agley."