In another respect, any social group (especially a complex, one) has many things happening at the same time. In such situations it's difficult for the researcher to observe everyone and decisions have to be made about who to observe and when to observe them - significant evidence may be  missed, leading to invalid interpretations of the group's behaviour).

Finally, human interaction is usually very complex - even in relatively simple forms of everyday behaviour. Just as we can "misunderstand" behaviour in our everyday interactions, so too is it possible for the sociologist to misinterpret the significance of some forms of behaviour.