Not finishing a project or experiment doesn’t disqualify you from succeeding in your PhD. If you didn’t read a certain paper, or follow a line of thought to some kind of conclusion you don’t forfeit your viva. You might need to explain if something seems missing. That explanation might be best in your thesis, but it could also be required in your viva if your examiners ask about it.
The root question is always “Why?”
- Why didn’t you do it?
- Why didn’t you read that paper?
- Why weren’t you able to finish?
Unless the answer is “I was lazy” then an honest response is what your examiners want:
- “I didn’t know about that…”
- “I focussed on something else…”
- “I learned about it too late to include it…”
Develop your response further by talking about what you would have done or could have done, or what you might do differently. Talk about what you learned in the process.
In most cases, unless you were being lazy, “that one thing” will just be one more little thing in a big list of things that you might have done during your PhD.
As you get ready for your viva it’s probably better – for your preparation and your confidence – to focus on what you have done, rather than on what you could have done.