得 opens onto a verdict on the action (寫得很漂亮 = how the writing came out); 結果補語 fuses an outcome straight to the verb with no 得 (寫完 = the writing got finished). Verdict behind 得, completed outcome without it.
V 得 + 補語 rates an action that happened (跑得很快 = ran fast); V 得 + result rates whether it can reach the result (跑得到 = can make it). One judges the manner, the other judges the possibility.
no 得: 她寫字漂亮 → 她寫字寫得很漂亮
object between verb and 得: 他寫得字很漂亮 → 他寫字寫得很漂亮
negation on the verb: 他不跑得快 → 他跑得不快 (negate the verdict, not the verb)
English puts the adverb before or near the verb (writes beautifully); learners front the manner word or drop 得, never letting the verdict ride behind the verb.