We　investigate　why　the　non-slip　boundary　condition　for　the　velocity,　imposed　in　the　direction　of　impressed　magnetic　fields,　can　contribute　to　the　magnetic　inhibition　effect　based　on　the　magnetic　Rayleigh-Taylor　(abbr.　NMRT)　problem　in　nonhomogeneous　incompressible　non-resistive　magnetohydrodynamic　(abbr.　MHD)　fluids.　Exploiting　an　infinitesimal　method　in　Lagrangian　coordinates,　the　idea　of　(equivalent)　magnetic　tension,　and　the　differential　version　of　magnetic　flux　conservation,　we　give　an　explanation　of　a　physical　mechanism　for　the　magnetic　inhibition　phenomenon　in　a　non-resistive　MHD　fluid.　Moreover,　we　find　that　the　magnetic　energy　in　the　non-resistive　MHD　fluid　depends　on　the　displacement　of　fluid　particles,　and　thus　can　be　regarded　as　elastic　potential　energy.　Motivated　by　this　observation,　we　further　use　the　well-known　minimum　potential　energy　principle　to　explain　the　physical　meaning　of　the　stability/instability　criteria　in　the　NMRT　problem.　As　a　result　of　the　analysis,　we　further　extend　the　results　on　the　NMRT　problem　to　the　stratified　MHD　fluid　case.　We　point　out　that　our　magnetic　inhibition　theory　can　be　used　to　explain　the　inhibition　phenomenon　of　other　flow　instabilities,　such　as　thermal　instability,　magnetic　buoyancy　instability,　and　so　on,　by　impressed　magnetic　fields　in　non-resistive　MHD　fluids.