The typical offenders are:
Have you applied the scale on your object?
Remove doubles. In Edit Mode, select everything with A and M to merge by distance
Flipped normals. Check if you have flipped faces. In the overlays you can turn on Face Orientation and if you see a red face, then in edit mode select everything and Shift + N to recalculate the normals
Check for interior faces or ripped vertices.
Also the angle of the face can be off. That is a tricky one and we can jump into that if non of the above work.
