Here’s a demonstration of just how important a role aperture, lighting, and freshness of film can play in your shots.

The left photo was taken with the aperture wide open at F2.8, the right one – at F8.0

The shots were taken only 3 seconds apart, but the results are very different.
The left one had direct sunlight hitting the house, while on the right one the sun hid behind a cloud

The left photo was a freshly bought roll of Portra 400, while the right one has been expired for about one year.