Can't extend line segment

Hi. Illustrator newbie here. I'm sure the answer to this question is remarkably simple, but I am baffled. I have created a set of stylized quotation marks. None of the paths is compound. I find that I must extend the long segment to the right. I do not want to change the scale, only extend that long segment.

I have tried clicking the rightmost anchor point and then dragging by using:

• The selection tool (black arrow)
• The direct selection tool (white arrow)
• The pen tool (the pen tool specifically) and not the other pen tools in the collection.

I have also tried dragging a marquee that crosses the specific line segment using the direct selection tool (per Adobe instructions on how to select a line segment).

None of my ham-handed and ignorant attempts at extending this straight line segment in what -- to me -- seems a direct and logical way appears to work. The pen tool created a line segment (in blue) but provided no apparent way to stroke it.

What is the secret? How can I extend this line segment to the right?

Thanks for any help on this holiday weekend. Stay well.

-j