keep the doors open

Somebody once told me to always keep the doors open. I think what he meant by this is to always do the best you can and the more you excel, the more doors will be open or opportunities will be available. However, if you shut a door or not take advantage of an opportunity, sometimes these doors are impossible to reopen. I know of people who kept doors open and did the best they could during college who are now succeeding in their lives. I know one person who in their 30s decided to go to medical school and another in their 40s who decided to go to law school. They were able to do this because they did well back in their college years and their efforts in college enabled them to make career changes and get accepted into graduate programs. Keep the doors open might sound like kind of a vague expression, but I definitely think I understand what that man was talking about.