Explanation
-길래 gives the reason for the speaker's own action as something they noticed: the first clause is what they saw or heard, the second is what they did about it. It attaches straight to the stem (있다 → 있길래, 예쁘다 → 예쁘길래, past -았/었길래) and is spoken and casual; -아/어서 is the neutral choice, and -기에 is its written form. 비가 오길래 우산을 가져왔어요 — It was raining, so I brought an umbrella.