Excuses & Reasons
When you explain why something didn’t work out in your research are you making excuses or sharing reasons?
They’re more or less the same in the context of justifying why or how you did (or didn’t do) something. The difference is what those words mean for you.
They make a difference at the viva too in terms of how your examiners hear your explanations.
Listing excuses will not help you. Finding reasons will help convince.
You’ll convince yourself first of all that you did the work and did it well enough. That will help you find the words to convince your examiners.