Why do the bad bits feel worse than the good bits feel good?

Today started with the mother of a child in L's class, someone I have known for maybe four weeks but who I had been surprised and delighted to find was treating me as a friend, undermining all the fragile confidence I had in that friendship by asking to borrow money.

Ten hours later and three of my children are upstairs wailing, where they have been banished for fighting, while I sit on the floor, nursing the sore elbow I thumped into the worktop, rather than any one of the girls, and waiting angrily to see what half an hour in the microwave does to a really beautiful and expensive bit of beef that is unaccountably still frozen solid despite eight hours in the warmth of the kitchen.

B is out rehearsing. I am home alone wishing I was anywhere else.

And in between we have been for a bike ride, watched a film, played pirates on the ship in the park, and generally muddled through with a minimum of shouting and a decent number of smiles, giggles and, at the risk of sounding cringy, love.

So not a bad day, really. None of the bad bits were that bad, and some of the good bits - S has really mastered balancing on her bike - were truly special.

So why, sitting on the floor, with A, now, cuddled up next to me, does it feel like such a bad day? Why do the bad bits linger and the good bits get forgotten?

And how do I turn that around?