Having my own back vs lying to myself

I had a very important meeting this afternoon and feel horrible about it. Instead of clearly explaining my point of view I was hesitant and unclear and it feels like I undermined my position.
How can I have my own back and still take responsibility for the situation (and learn from it?)?
C: I said: I don‘t know what position I want
T: I should have thought it through before
F: self loathing, shame
A: cry
R: feel weak