I think what he misunderstood was that if you have an overall gain then the carryover can be used to the extent of the gain. So if you have a net gain of $5,000 and the carryover is $10,000 the gain is wiped out and you have an overall loss of $5,000 of which you can only take $3,000 that year against other income so the following year you will only have $2,000 carry over. You can't however not take the $3,000 against other income unless there is no other income.
I am sure I did not explain that very well.