Add a perspective
Your input
I am putting together my design portfolio. Should I include unfinished projects if I explain what I learned from them?
Your point of view, optional
I think the decision process is useful when the lessons are clear. Do not invent a personal experience.
One way to phrase it
I’d include an unfinished project if it shows a decision you made and what you learned from it. What would you want someone reviewing your portfolio to understand?
It answers the actual question and invites a useful follow up, without inventing a project detail.