Depends on the situations. Here's a few.
Part One... Acute
1) I don't. I say I'm really sad/disappointed/etc. right now
2) And then I tell him the same thing I tell him to do when he's sad/disappointed/angry/etc. (mine wouldn't apply here, what do YOU tell your kids when they're having a rough time?), except I say 'Mom needs to..."
= GREAT modeling, teaching/allowing for compassion/etc.
Part Two ... Fake it till I make it OR Silver linings
1) I find the happy. Right now (pending investigation that's FINALLY starting over 6mo after the fact) the courts have my son with his abusive dad 50% of the time. I HATE this. And I know that every time he goes to his dads the next time I see him may be in the morgue. So do I show ANY of that? Serves no purpose. So I find the happy. I HOPE he'll have a good week. And when he comes home excited that dad 'only' called me (mom) a C-word 3 times this week... I'm happy for him. (Should be blood boiling that it's happening at all... But HE's happy, because it's better, so I'm happy for him. Any straw or silver lining I can find I grasp at it.
PART 3 ... So bad it serves no purpose
1) Outright denial. I stick xyz in a box and stuff it so far down I cross the dateline.
2) Intentional avoidance. AKA A babysitter while I fall apart in private. Occasionally overnight. Complete meltdown over, I'm able to put my mom hat back on.
Part 4... Which way do you want to go? Up? Or Down? /AKA choosing perspective
1) Faith / Belief / Pick your word. My son amost died (hospital sick) a LOT last year. Did I ever tell him? Nope! BELIEVING you're going to recover / everything will work out is a nuke in your arsenal. So I believed it for him, so he'd believe it, too.
2) How can we make ?!?!?!?!? Okay..No heat this winter. Could have pitched a fit. Instead (after calling my attorney to let them know DH was screwing around getting our heat shut off)... We put on snow suits and baked cookies and had a superfund day. A weird, bizzare, unusual day.. But a good one. At Children's hospital last year, my son could walk (or do fun chair tricks... O2 too low, we had chair, oxygen tank, and IVs anytime we left the room. He wanted to play sooo badly. So I took my phone and took pictures all over the hospital & we did a scavenger hunt. Could have just sat in the room. Could have just gone in circles. Instead... Came up with a game he COULD do
_________
Most of these boil down to: Improvise. Adapt. Overcome.