A good impression deserves time before it becomes a complete account of someone.

First impressions harden fast, and pleasant ones harden fastest because nothing pushes back. Someone is warm, funny, quick, and within a week you have written the rest of the character from that opening: reliable, honest, good in a crisis, none of which you have seen. What happens is that a small sample gets promoted to a full portrait, and later evidence has to fight the portrait to be admitted.

Hold the good impression as a beginning rather than a conclusion. Let time and ordinary situations add to it, particularly the dull ones. Extend warmth freely and reliance more slowly, since the two need not move at the same speed.