Difference between “First and last” and “First or last”

first and last—

1. coming before anything else in order, rank, etc.:

• They say that exquisite painting is the first and last business of a painter.

2. in essence; for the most part:

• You are a scientist first and last. Your other activities are merely field tests of the work you do here.

Note: The expression does not correlate in meaning with the phrase from first to last—from beginning to end; all along:

• A clever coach was able to advise them from first to last and the crew have improved steadily.

first or last—is used to express indifference as to order:

• You may do it first or last; I’m sure I don’t care as long as you do do it.