There can be many factor at play. The most common cause are non normals, such as reopening a door or a return to gate however simple motor actions or distractions can and do occur.
My airline commissioned an investigation into accidental door deployments and now instead of just checking doors are disarmed following the trigger to disarm the doors, crew are asked to disarm doors at a different time compared to before (now done when pax are still belted in), and doors are checked with a 'stop check' so two crew members are involved in opening the door. Accidental door deployments are significantly reduced.