My team uses the typical Kanban categories: To-Do, In-Work, Waiting, and Done. A good rule of thumb is that a person should keep no more than three items in the To-Do column.
In an ideal workflow, the only reason something should be in the In-Work column is that the person ran out of time or energy to finish it in the moment. Otherwise, they should continue working on the task until it can be moved to Done or Waiting. The only situation where someone might have more than one item in In-Work is when a higher-priority task is assigned unexpectedly.
From another perspective, having more than three items in In-Work may indicate that you’re trying to juggle too many tasks at once or that you’re avoiding a specific task. Over time, this will reduce productivity and slow down overall progress.