The proof of the pudding (is in the eating).

something that you say which means that you cannot judge the value of something until you have tried it.

I've read the proposal and it looks promising, but the proof of the pudding is in the eating.

• cut out for something
• cut out something
• cut own throat
• cut someone dead
• cut someone down to size
• cut someone loose
• cut someone some slack
• cut someone to the quick
• cut some slack
• cut something down to size
• cut something loose
• cut teeth
• cut teeth in
• cut teeth in something
• cut the cord
• cut the crap
• Cut the crap!
• cut the Gordian knot
• cut the ground from under feet
• cut the ground from under someone feet
• cut the ground from under someone's feet
• cut the umbilical cord
• cut things fine
• cut through
• cut through like a hot knife through butter