Also, for one thing. As the first of several possible instances. For example, Everything seemed to go wrong; for one, we had a flat tire, and then we lost the keys, or I find many aspects of your proposal to be inadequate; for one thing, you don't specify where you'll get the money. For one can also be applied to a person, as in He doesn't like their behavior, and I for one agree with him.
|as a particular one of several possibilities; "I for one feel very grateful"; "her mother for one was worried"|