With a trailing drawdown, the breach level follows your high-water mark. If the limit is $2,500 and you make $1,000, the breach level rises by $1,000 too. Some firms trail on closed balance, others on live equity (including open profit), which is far harsher. Many stop trailing once it reaches the starting balance.
It is the single most misunderstood prop rule and the one that ends most funded accounts.
Example: $50,000 account, $2,000 trailing drawdown. You run up to $53,000 intraday on an unrealized gain; the breach level is now $51,000. You close the trade at $51,500. Any further loss of $500 ends the account.
Related: static-drawdown, daily-drawdown, max-drawdown, evaluation