It’s like adding wood to a fire that is already burning well. Adding wood to a fire that has gone out is pointless — that’s the “buy more at a loss” trap from course 6.
Example. You bought at $100, stop at $97, risk $30. The price reached $106 and made a new swing low at $103. You move the stop of the first part up to $102: with normal price moves, it can no longer go into a loss. Now you add a second, smaller part: 5 units at $106 with the same stop at $102. Its risk is 5 × $4 = $20, and that’s less than the original $30. Traders call this technique pyramiding.