Learn to Use your Computer

Drag-and-drop in Insert mode is one of Excel's more finicky features. Sometimes, you do everything just right and you still get the alert box indicating that Excel is about to replace existing entries instead of pushing them aside (always click the Cancel button). Fortunately, you can insert things with the Cut (Ctrl, X) and Insert Paste (Ctrl, V) commands without worrying about which way the I-beam selection goes