Often times when I attempt to edit text within a cell in Excel, double clicking the cell doesn’t get me into text mode, which can be very frustrating. This often happens in Visio as well when I go to edit text within a shape.
Instead of double clicking within a cell (or shape if you’re a Visio user), simply select the cell and press F2. This will get you into text mode where you can edit away. When you’re done, press Esc to leave text mode. Much simpler that the double click!