Legitimate or not, big or small, every excuse has a tolerance point.
Don't abuse the patience of those who give you the benefit of the doubt. The people that understood you when the world was ending, also know you well enough to spot when you are bullshitting them.
Every time you use a reason it converts itself closer and closer to an excuse. To the people that understand you, it's an excuse not to learn, grow, or take the next step.
The sooner you realize that people understand you, the better chance you have to save the relationships(professional and personal) that are worthwhile. If not, you are going to find that you have been written off a long time ago.