The honest answer, according to major health authorities, is that most lower back pain is classified as 'nonspecific' — meaning no single structural cause can be identified on imaging.
Why 'nonspecific' doesn't mean 'not real'
Mayo Clinic's overview notes that back pain often results from a mix of muscle or ligament strain, poor conditioning, and posture — factors that don't always show up clearly on an X-ray or MRI, but are still genuinely painful and treatable.
Common contributing factors
Weak core muscles, tight hamstrings or hip flexors, prolonged poor posture, and general deconditioning from inactivity are the most commonly cited contributing factors — many of which respond well to consistent gentle movement.
Why imaging isn't always the answer
Structural findings on imaging (like mild disc bulges) are extremely common even in people with no pain at all, which is part of why major guidelines increasingly emphasize movement-based treatment over imaging-driven diagnosis for typical low back pain.
Should you get an MRI for ordinary lower back pain?
Current major guidelines generally recommend against routine imaging for typical low back pain without red-flag symptoms, since imaging findings often don't change treatment and can even lead to unnecessary anxiety or intervention.