How often have you found your own name spelt incorrectly on a document or when written down by someone else? I’m sure it’s happened!
Your ancestors likely had the same problems, plus they may have had limited reading and writing skills or been illiterate, the names may have been written by others such as the vicar who didn’t always know how your ancestors name should have been spelt and sometimes words may have been written as they sounded. Also check out known nicknames for that name or that you know your ancestor was known by and don’t forget possible abbreviations of the name. Consider how the name may have sounded when said in a different accent. Try different vowels in place of the ones that are in the name.
When you can’t find your ancestor, think outside of the box. It’s important to be creative when searching!