When setting up a cycle, you can define all or only some questions as optional questions. This might be useful if you think that not every contributor will be able to answer every question.
To do so, choose "Show N/A" for a competence based question or "Optional" for a custom question when setting up the questions for the cycle. As a consequence, contributors will be able to choose "Not applicable" instead of picking a scale value when they feel that they cannot answer the question.
If you don't choose this option, the question will be mandatory and cannot be skipped.
You can always come back to these settings later and change them - even after the cycle kickoff. This makes it possible to activate the N/A option at a later time in the process, e.g., when some of the contributors tell you that they found it hard to answer each and every question. If you do so, the changes will be active immediately in all questionnaires, even those that have already been started.