You imagine a line that goes to negative values to the left positive values to the right and 0 for the present tense. Past Simple happens in the negative zone and does not touch to 0. However, the present perfect started in the negative value zone and crossed to the positive values. Therefore, it affects the present. However, the simple past does not affect the present. For example; Past Simple: I washed my face. (It dried probably) Present Perfect. I have washed my face. (It is still wet.)