Why it feels smart and isn't
The logic sounds reasonable in the moment: "the price is lower now, so if I buy more here, my average entry improves, and I only need a smaller bounce to break even." The problem is that this logic has nothing to do with why the price moved against you in the first place. The market doesn't know your average price and doesn't owe you a bounce.
Averaging down turns one small, planned loss (respecting your original stop loss) into a much larger position that keeps growing every time the price keeps falling — exactly when your account can least afford it. It is the single most common way a manageable -1% trade becomes a -20% or account-blowing one.
The fix is boring on purpose: decide your position size and stop loss before you enter, and let the stop loss do its job if it's hit. If you still believe in the trade afterward, that's a brand-new decision with its own fresh risk sizing — not a rescue mission for the old one.