When selecting portions of text, Word tries to be helpful by predicting what you want to select. If you click in the middle of a word and then drag to the next word, Word will increase the selection to include all of the first word. For example, if you click between the two l’s in the word magically (below) and then slide into the next word, print, Word automatically extends the selection to consume all of magically, whether you meant to or not.

If you back-drag the selection, Word will undo the automatic selection, but that’s a nuisance. To countermand Word’s behavior for the current selection, hold down [Shift]+[Ctrl] before making your selection. Then, Word will limit the selection to only those characters you actually drag across.
You might find yourself overriding the automatic selection behavior more often than not. When this happens, consider disabling the feature as follows:

  1. From the Tools menu, choose Options.
  2. Click the Edit tab.
  3. Clear the When Selecting, Automatically Select Entire Word option.
  4. Click OK.