Quite early in my research, I followed the wrong family.
Christopher Alston married Emily Fulham in late 1891, but I had trouble finding him in the 1891 census.
However, in 1881, there was Christopher only 4 miles away, with a different occupation and his age just a couple of years out, and a father with the right name and occupation to match the marriage. Well we all know of people whose ages are variable, and a teenager can easily end up with a different trade.
I traced this family back another generation or so, then searched the 1891 census more carefully for Christopher, who was no longer living with his now-widowed mother.
And I found him, as Christopher AUSTIN, living with his widowed father, within walking distance of his future bride. Right age and occupations too.
They were the AUSTIN family in 1881 and 1871 too. I was somewhat stunned. I'm not who I thought I was!
In 1861 though, it was AUSTEAD.
So I pruned a fair slice of my tree and started growing it afresh. I now know that my surname started out as Halstead, and it changed to Alston because that is what the priest THOUGHT he heard in 1891.