I can't go through with it - This is for people who talk the talk but can't walk the walk

This is for people who talk the talk but can't walk the walk. It's like saying you're a beast but then running away when the other guy shows up.

'I can't go through with it' said when he had to talk to the principal.

'I can't go through with it' said when she had to give a speech in front of everyone.

'I can't go through with it' said when he had to do the big presentation.