Here is an interesting expression for you: “where the rubber hits the road” or “where the rubber meets the road”.
It is a useful little idiom which – unsurprisingly – originated from racing. When the rubber of the tires hits the road, that’s when the car starts moving.
It is now used much more broadly and with different meanings in different contexts. So it isn’t easy to give a comprehensive explanation of this idiom. Let’s try, though:
It can mean “when things get serious” or indicate the point at which reality must be faced, or the point at which a decision or a stand must be taken, the time when talking stops and the action must begin.
Some examples:
“This strategy sounds very promising but it’s the implementation of these ideas where the rubber meets the road.”
“You have to stand by your spouse not just in good times but also through bad times. That’s where the rubber hits the road.”
An example from recent politics in the UK: “David Cameron today warned his Cabinet ‘this is where the rubber hits the road’ as the Government prepares itself to unveil swingeing spending cuts within weeks.”