Why is it wrong to use if here，in golang，remove-duplicates-from-sorted-array

1. I am a beginner and hope to get your help

2. it is remove-duplicates-from-sorted-array

   func remove(nums []int)int{
    i,j:= 0,0
   
   
    //Why is it wrong to use if here？
    // if j< len(nums)
    for j < len(nums){
        if i==0 || nums[i-1]!= nums[j]{
            nums[i] = nums[j]
            i++
            j++
        }else{
            j++
        }
    }
    return i
   

   }

     func main(){
        nums := []int{1,2,2,3,5,5}
        result := remove(nums)
        fmt.Println(result)
      }
   

3. please help me