I've only come to understand 'Don't share your plans with everyone' in my later years, and have heard it echoed by many, many people who have been in the situations I understood it best applied to: Escaping the dangers of Narcissists and Predators around you.

Don't tell your abusive girlfriend you're getting therapy, don't tell your mother you have money saved for rent, don't tell people who are negative and want you to remain their servant that you've got plans to go to college.

Any saying that is a truism, is usually a generalizations, because generalizations come with many, many exceptions. Don't share your plans with EVERYONE. Share them with those you trust. I hope that makes more sense.