When you are drawing with the Adobe pen tool, keep an eye on those small modifiers that appear in the lower-right of the pen icon. They change as you use the pen tool depending on what you do or which part of a path you hover over.

If you are new to the pen tool (or want a quick refresher) print this handy cheat sheet and train yourself to pay attention to the subtle cursor changes. Once you get to know them, the different icons remind you of the action you are about to perform.