While we, especially Sherry, focus on common grammar errors, my book (Literally, the Best Language Book Ever) discusses words or phrases that should be avoided for other reasons. That brings me to any sentence that begins with the phrase One of your problems is…. Don’t ever say that unless you’re a psychiatrist, and a patient asks you for a diagnosis.
Seriously, no one likes to have his flaws brought to his attention, and besides, who are you to decide what problems another person has? Focus on your own problems, not someone else’s.
If a co-worker or member of your family is saying something that you believe is illogical, then tell the person why you think the statement is illogical, such as I think you need to consider how much money this is going to cost. Avoid, however, making general statements about the person’s approach, such as One of your problems is that you never think about how much things will cost. That’s not going to help with the specific situation, it’s probably not always accurate, and it’s going to sound condescending.
What amuses me most is when this statement is turned into a question, as in Do you know what one of your problems is? When people ask me, I say No, and I don’t want you to tell me.