To the parents who have disappointed DC right now...(you may not be posting, but you may be reading this thread).
I got 12 A-stars at GCSE (A-star was relatively new at the time, so maybe it was easier).
I then performed terribly in my A-Levels TWICE (I have 8 A-Levels, none above a D, several Ns and a U). I just didn't work hard enough and then cracked under the pressure. I was so disappointed in myself, and my parents were so disappointed in me.
But I'm now 45, I am in an executive-leadership role, doing a job I love, my base salary is over £200K (which is why I name changed) - I own a home, I have a family, and I have a really happy, settled, life.
Of course life's not perfect, but my A-Levels no longer play on my mind as a time I failed.
Even if today is disappointing, even if your child needs to change direction - please know that there is huge scope for professional success and happiness.