The hardest for me is when I need to keep a secret from my husband. THat is a secret a mutual friend has told me. Essentially I tell my husband everything or most of everything, but sometimes he might ask do you know what is going on with person A/B or C, and I do.... but... I usually respond yes but it was told to me in confidence....
I was a blonde at one time, now I am just grey

and I like to forget what folks tell me, safer that way as I can't blurt out confidences.
And some matters are just very very private, and if you want to keep them that way, tell only your therapist or as some-one said your animals