The nail on the left is exposed, leaving it open to rainwater.
The nail on the right has punched through the shingle, leaving an open hole for water penetration.
This is an incorrect stagger. The correct stagger would look like a stair step every 6 inches. Here you can see its back and forth, leaving the shingles in straight rows.
Random damaged shingles.
Random shingles need to be replaced.
Valley has woven incorrectly.
The top of the valley is cut bottom is woven. It should be one of the 2, not both. Now water can run under the bottom woven shingles. Both valleys are like this.
Visual Marketing By Lead Symphony – Patent Pending