Modifiers on a 3D model might not show due to disabled viewport visibility, unapplied modifiers, or viewport mode issues. If a modifier’s "Show in Viewport" toggle is off, its effect won’t appear. Some modifiers also need to be "Applied" to become permanent. Using wireframe instead of solid view, or minor glitches, can also hide effects. Try checking the modifier’s visibility setting, switching to solid view, or reapplying it—these quick steps usually fix the issue.
