Unconsciously we commit mistakes while writing something.Simple mistakes can cause great damages. One should be very careful with silly errors.
For instance 'your', possessive pronoun sounds like 'you're' but has different meanings. 'You're' is a combination of 'you are'. Similarly in the case of 'it's' and 'its' and 'they're', there and their.
We often get confused in using 'affect' and 'effect'. Both 'effect' and 'affect' are considered as noun and verb. Because of similarity in pronunciation, it's hard use them. They both more or less signify 'influence'.