A strange problem when I wrote a simple surfaceshader using Occlusion

Here is my surf function:

     void surf (Input IN, inout SurfaceOutputStandardSpecular o)
     {
         fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
         o.Albedo = c.rgb;
         o.Specular = tex2D (_SpecGlossMap, IN.uv_SpecGlossMap);
         o.Smoothness = _Glossiness;
         
         half occ = tex2D(_OcclusionMap, IN.uv2_OcclusionMap).g;
         half oneMinusT = 1 - _OcclusionStrength;
         o.Occlusion =  saturate(oneMinusT + occ * _OcclusionStrength);
         
         //Magic?????????
         half noMatterWhat = 10000;
         if (o.Occlusion == noMatterWhat)
         {
             o.Albedo = o.Albedo;
         }
         //End
         
         o.Emission = _EmissionColor;
         float4 packedNormal = tex2D(_BumpMap, IN.uv_BumpMap);
         o.Normal = UnpackNormal(packedNormal);
         o.Alpha = c.a;
     }

If I delete the "Magic" part, the model becomes tatolly dark.The param "noMatterWhat" could be any number, it works. As you can see, the "Magic" part actually does not play any role. But why this happens?