"Self-assured" vs. "self-confident"

Where self-assured is 'sure of yourself,' relates to you and your actions (it also comes with a minor connotation of pride), self-confident is confidence in one's abilities and relates more to your mind.

They may be used interchangeably, (m-w.com defines self-assured as self-confident), but there are minor differences in tone that can affect your reader.

Self-assurance can sometimes make you give yourself too much credit, which, if you're not careful, can touch pride

However, with self-confidence, you don't have to give yourself credit, because you know your own strengths and abilities, so you've already got enough