To make all of this even more confusing, the word 잘못 (with no space between 잘 and 못) has a different meaning. 잘못 means "mistake." This word would normally be an easy word to deal with. However, it is more difficult than it needs to be because 잘못 and 잘 못 have two different meanings. 잘못 can be used like this:
그것은 제 잘못이었어요 - That was my fault/my mistake
Normally when you say "my _____" you use 저의 or 나의. However, some nouns prefer to have 제 and 내 before them instead of 저의/나의. 잘못 is one of these nouns. Another example is 제/내 생각 (instead of 저의/나의 생각) meaning "my thought/my opinion/what I think."

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LEARN KOREAN (한국어) [GRAMMAR] #1
RandomThis is book #1 for the Korean Language series. Try to understand all of the notes in this book before you proceed to the next one. Good luck ! This book contains Korean grammar. Try to understand it so that you can understand how to make a sentence...