If you are in England of English descent you can generally go back through official and Church Registers to 1558 (Elizabeth I) and perhaps 1538 (Henry VIII) who both mandated the keeping of Parish Registers. Baptisms, marriages and burials are recorded with varying levels of supporting contextual information. You might not be able to on some lines due to missing documents or uncertainty over who was who in a parish due to duplicate names alive at the same time or people moving out of area. However, you'll probably get back to one of these early registers on one line if you research thoroughly and cross reference against other documentation like Court records.
So what happens when you cross the 'alive at 1538 / 1558' threshold? You lose the continuity in tracing the common and middling people because there are hardly any records for them that can be put together to create a genealogy.
Not so with the significant landowners. Your aristocratic families keep pedigrees (which can sometimes be erroneous and often like to go back way beyond WTC et al to mythical Kings). However, they are generally pretty good and due to intermarriages can be cross referenced between families. Add in records for wills, land transfers etc. and Church office holders, who are often the other non-inheriting sons, and you can go back from 1558/38 to 1066-ish. They keep the pedigrees because they need to prove legitimate title to inherited lands, noble titles, rights and occasionally offices.
Therefore, if you can pass through the 'alive at 1538/58' barrier then you enter records for the elite. Guess what these generally Norman and allied types do? They inter-marry. So pass the barrier and after a couple of centuries in this 500 year or so zone you will find massively shared heritage. Therefore being descended from WTC or others shown to hold land in the Domesday Book of 1084 is not surprising.
It's an elite though. Early on there were marriages with the same French speaking Scandinavian-French hybrid ethnicity in Normandy and around, and of course the royals marry with other royal families in Europe in a wider elite. There's a discontinuity with the English pre 1066 because William's power grab is largely a decapitation and replacement of the English elite by Normans, Bretons and Flemings. If you have 1066-1084 Norman ancestry you won't get much further than a father and perhaps a grandfather at best (unless you are William and you can go back further).