Bit seems to number the item in question as being a single item. This seems a little bit contradictory as my initial impression is that bit works best when speaking about uncountable things. Like 'you've got a bit of flour on your jacket.' So these are not singular in the individual items as an individual piece of flour is so small you wouldn't even see it. It might represent a single patch though. I might say you have a little flour on your jacket and I could certainly say that there is a little dust on the monitor but I would definitely be more likely to say there is a bit of dust on the monitor. Bit is definitely a way of saying a piece. Bit = Piece. Little is definitely a way of saying small. Little = Small. I think the confusion comes in when a person has a bit of flour on their clothes one might say 'you have a little bit of flour on your jacket'. They therefore can commonly go hand in hand to make one expression. Bit meaning one patch and little meaning the patch described by the word 'bit' is not a large patch. Over time I would guess that the language has become a lot lazier and people cut words out so sometimes one goes and sometimes the other. Often they are still used together to say things like 'I have probably been thinking about this a little bit too much.' I could of course also say 'I have been thinking about it a bit too much.' I would not say 'I have been thinking about this a little too much' At least I would certainly not say it very often. I would not rule out saying it, but it does sound strange to use. Naturally if I say a 'bit too much' I am talking about it as a certain amount of too much. If I say a 'little bit too much' I am probably trying to underplay quite how much I have thought about it. In general everyone knows I have been thinking about it far too much but I am basically saying 'no not that much, not really, only a little bit.' The word 'bit' apparently is very closely related to the word 'bite' One can imagine a bit as being like a mouthful. When you bite something you essentially cut off one bit of that thing. The word 'little' on the other hand has alway been about size or distance. The two have certainly grown closer together with use though. In Robin Hood there was a character called Little John on account of the fact that he was actually very big. Aside from the use of bit to describe a quantity of one it is also used to describe a number of things that are individual things, i.e. without complicated machinery, etc. A drill bit for instance is the piece of metal that actually goes in the end of the drill. Another example is the bit that it put in a horse's mouth when you are riding. I think the Americans also refer to some coins as being bits.