kǔ sī 
		to think hard
bitter thoughts
to pour out one's sufferings
		 
		
		
		
		
			 
		
				
		
			kǔ sī míng xiǎng 
		to consider from all angles (idiom); to think hard
to rack one's brains
		 
		
		
														
		
		
			 
		
				
		
			yì kǔ sī tián 
		to view one's past as miserable and one's present as happy (idiom)
		 
		
		
														
		
		
					
				
		
			láo xīn kǔ sī 
		to rack one's brains
to think hard