Nearly every house in Santa Cruz County has a few drywall cracks. Houses settle, lumber shrinks as it dries, and the ground here moves. Most of these cracks are cosmetic, but a few are worth looking at more closely before you patch them.
Thin cracks running off the corners of doors and windows are usually settling. Nail pops, the small round bumps in a wall or ceiling, happen when framing lumber shrinks and pushes the fastener out. Both are straightforward repairs: reset or replace the fastener, tape, mud, match the texture, and paint.
Be more cautious with cracks that keep growing, doors that suddenly stick, or cracks paired with stains. Growing cracks can point to a framing or foundation issue, and stains almost always mean water. Patching over either one just hides the problem for a while.
The key to a repair that disappears is texture matching. Orange peel, knockdown, and smooth walls each need a different technique, and a patch that doesn't match stands out in afternoon light. If you're not sure what's behind a crack, have someone look before you paint over it.