List index out of bounds whilst deleting items

Question

I solved my problem but I need to know why this problem raised to me ?!

I write a project that load file to listBox then delete the strings one by one,

but w

Answer 1

There may be situation when you DO NOT delete certain items. Then the generic approach would be

i := 0;
while i < ListBox3.Items.Count do
  begin
    ShowMessage(ListBox3.Items[i]);
    if  then // some condition there
      ListBox3.Items.Delete(i)
    else
      Inc(i);
   end;