Many families have their own traditional names which are passed down generation by generation and occur frequently in the family tree. In many countries there are naming traditions that are frequently followed, some of which might seem quite strange to us today. There are names which go in and out of fashion, especially in response to Monarchs and other prominent people of the time.
In my own family, one naming tradition which took me aback when I first encountered it was the habit of reusing a name given to a dead child. In my Green family a few generations back I have three Isaacs in one generation - the first two died young and the name was reused for the next-born son each time. Eventually persistence paid off and the third Isaac Green in that family lived well into his 90's. His father was named Isaac as well, and the name crops up in several other generations. In my mother's Pummeroy family William and Alfred are popular, and recur several time across the generations. This can create an additional challenge in making sure any information I find is linked to the correct person - I have a newspaper article from Trove that mentions William Pummeroy - and I have four of them alive at the time that the article could be referring to!
In my Irish family line, the tradition of naming the first son for the paternal grandfather (not a habit unique to Ireland by any means) also causes me headaches. My ancestor James Mulholland had 5 sons, 4 of them living to adulthood. These 4 adult sons - James, Patrick, David and Henry, ALL went and named their first son James! As they all lived in fairly close proximity, this means I have 4 men named James Mulholland living within a few miles of each other, born within 5 years of each other - and two of them married women named Mary.
Abbreviations and nicknames also complicate my research - my father's second brother Ernest was always known as Squib, sometimes even on official documents. In my mother's family, I have great- aunts Thelma, known as Lalla ; Elizabeth, known as Betty and Pricilla, known as Illa. Another Elizabeth, in my father's family, was always known as Betsy, even in census records, on her children's baptism records and on her own death record.
All these various name usages can throw up roadblocks and cause mistakes in my research. Recurring names make it difficult to ensure I am researching the correct person any time I locate new information, and nicknames, spelling changes and wholesale name changes can mean I completely miss relevant records because I don't know the name variation used at the time.