Though it is not impossible to trace back to the 11th century, the task obviously becomes far more difficult the further back in time one travels.
Not the least of one's problems being the level of intelligence, writing ability and accuracy of those responsible for whatever records were made of births, marriages, and deaths, if the record was made at all.
Another problem often found to impede access to information is that of the family's surname. A common surname will eventually present many difficulties as one begins to sort through the hundreds of Smiths, Joneses, and other such names that have survived the passage of time almost unchanged.
An unusual name however, or one known to originate from a particular region, and your task becomes far, easier. Some names also stem from the family's primary occupation as we discussed earlier.