A line of the poem "To A Mouse" is often quoted: "The best laid schemes o' Mice an' Men" to mean that well-planned plans can go wrong.

	But, Mousie, thou art no thy lane,
	In proving foresight may be vain; 
	The best laid schemes o' Mice an' Men,
	Gang aft agley,
	An' lea'e us nought but grief an' pain,
	For promis'd joy!

	-- "To A Mouse" by Robert Burns
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'Gang aft agley' is Scottish and means 'Often go wrong'. 

More directly translated:

*gang = 'to go'
*aft  = 'oft' (or often)
*agley = 'askew, awry' (i.e. wrong, badly. 'Gley' is 'squint', so more literally would be 'off squint')

'' 'Aft' in this context has no relation to the nautical meaning of 'aft', but is a Scottish form of 'oft'.''
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''Yet another example of documentation failure.'' See also: BigDesignUpFront
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''But, where is the part that interests mice?  Where is the part that says "Cheese is good."?''