I forgot about the sub-skills in my review. As RageRed and Equinox pointed out to me:
Sub-skills represent the activities for which ability checks are most often rolled during the course of a game. If you are proficient in a skill, you are also proficient in all the sub-skills.
Sub-skills include:
• Str (Athletics) sub-skills: Climb, Bend Bars, Wrestling.
• Dex (Sleight of Hand) sub-skills: Pick Locks, Disable Traps.
• Con (Survival) sub-skill: Track.
• Int (Arcana) sub-skills: Planes, Magic.
• Int (Investigation) sub-skills: Loot, Find Secret Doors.
• Wis (Perception) sub-skills: Vigilance, Locate Traps.