Hi. Just (yesterday) bought Civ 6 some 23 odd years since I last played it as Civ 2. Anyway this is probably a really dumb question but I cannot find the answer in the Civilopedia - so I very often just want a unit to stay where it is so I click 'skip turn' but sometimes, and I cant pinpoint why, I do not get this option so I either need to move or 'fortify' or 'Alert'. Obviously this is not a huge game breaker but I am curious as to why the option to 'skip turn' is sometimes missing.