Closing a figure drawn with Pen???

Dream_  schrieb Or how do you make symmetrical shapes you draw yourself?

Since this part of the question is a more general one, I'd like to add the most important part:

Make sure that things are aligned carefully. So when drawing the left part of the mirror, make sure that the points on the right side are aligned exactly.

And from then on I usually use the transform effect to create the mirroring. This allows me to adjust things while already working with the finished object.

I can still adjust the shape of the shield easily, because it's only one half drawn. The mirrored half will pick up any change immediately automatically. When I'm done: expand appearance (if needed).

But most important part: The two selected points need to be perfectly aligned. I use the align panel (only possible when there are more than 2 points on the path).

This may be overkill but how about making a teardrop from a Circle shape? Here are the directions.

Dropbox - Teardrop.pdf

Use your direct selection tool (located next to the selection tool. Keyboard shortcut is "A") and then select the points (make a bounding box around the two anchor points). Once you have the anchor points selected, (not the entire object)  the Control panel (just below menu) should show what is selected, which in this case is the Anchor Point. (See my earlier picture) The options to alter those points will be located there on the control panel.

Only two open points can join... don't select the center line. Remember every anchor point can only have two segments attached to it (based on basic geometry). That third line can not be connected to the other two segments. (It might be easier to move the third segment out of the way while you are joining the top of your teardrop) Once the teardrop is complete move the third segment back and try different caps to find the one that looks the best. Probably the rounded. (panel shown in one of the above answers)

Another way

Select both sides and using the Shape Builder tool drag the mouse cursor  across the shapes to unite then into one ..

In the screen shot below the process is shown:

In the first picture the end cap of the lines has been set as yours is. Change that to the round ends as in the second picture. In the third picture I've used the keyboard command Option/Alt-Command/Control-J to average both points bringing them together but as yet unjoined. In the last picture I've used the keyboard command Command/Control-J to join the two points.