Making a long entry when the cell’s width doesn’t accommodate the length may have unexpected results. If there’s no data to either side of the cell in which you’re entering the long string, Excel will display the entire string–Excel doesn’t care how long the string is or how many cells the string obscures.
When data exists to the side of the cell, Excel truncates the long string you’re entering. If you choose to, you can press Alt-Enter to position a carriage return in the cell. Then, you can continue typing the string. In addition, once you enter the multi-line string, the row will automatically adjust its height property so you can view the entire string.