Have you ever noticed that you can understand English grammar perfectly well and still avoid using it when you speak? I see this quite often with the Present Perfect. Students learn the tense, do the exercises, and get the answers right. Then we start talking, and suddenly the Past Simple appears in almost every sentence.

Imagine you're telling me about your day yesterday. You went to the supermarket, bought some milk, and came home. Nothing complicated there. You're telling me what happened, one thing after another.