Feudalism is the exchange of land for military service, thus everything was based on what was called the knight's fee , which was the amount of money and/or military service a fief was required to pay to support one knight. Thus, either a fief could provide the service of a knight, or an equivalent amount of money to allow a lord to hire a knight.
The knight's fee value of a fief varied based on the size and resources of a particular fief. The lord of Stafford, Robert of Stafford, was responsible for 60 knight's fees for his Stafford fief. Robert sub-let 51 of those 60 knight's fees in the form of 26 sub-fiefs, the largest fief provided 6 fees, while the smallest 2/3 of a fee. Thus in all, the 26 fiefs paid 51 fees. Further, some of these sub-fiefs had sub-sub-fiefs with fees of their own, and sometimes went a layer below that. In all, 78 fiefs were part of the Stafford estate, 26 of them reporting directly to Robert and the rest layers below. It was a system of tenants and leases and sub-tenants and sub-leases and so on, each layer reporting vassalage to the next layer up. The knight's fee was the common base unit of denomination. Often lords were not so much lords presiding over great estates, but managers of a network of tenants and sub-leases.
Some of the Stafford tenants were themselves lords, and this illustrates how complex the relationships of lord and vassal could become. Henry d'Oilly, who held 3fees from Robert of Stafford, also held over 30 fees elsewhere that had been granted to him directly by the king. Thus while Henry was the vassal of his lord Robert, Henry was himself a lord and had many sub-fiefs that he also managed. It would have also been possible and not uncommon for a situation where Robert of Stafford was a vassal of Henry elsewhere, creating the condition of mutual lordship/vassalage between the two. These complex relationships invariably created loyalty problems through conflicts of interests; to resolve this the concept of a liege lord was created, which meant that the vassal was loyal to his liege lord above all others no matter what. However, even this sometimes broke down when a vassal would pledge himself to more than one liege lord.
From the perspective of the smallest land owner, multiple networks of lordship were layered on the same small plot of land. A chronicle of the time says "different lordships lay on the land in different respects". Each lord laid claim to a certain aspect ofthe service from the land.