“We make a mess of things when we start lying.”

It’s written in an older English style. Essentially it’s just the first one you’ve mentioned.

The ‘first’ in the second half of the phrase isn’t relevant in current times but would have been common to include in sayings like this - it’s more noting that you have the intention of lying, not that you’ve found yourself doing so off the cuff.

It’s like this: “if you are going out there to lie about something, this is going to go to shit”. Rather than, “this is going to shit because it’s the first time you’re lying”, that’s a far too literal take on older English.

And for any non-native English speakers - ‘practice’ is the act of doing something, as opposed to ‘practise’ being learning/mastering through repetition.

I think it’s the first one. A lie starts small but can quickly grow out of control. It’s from the poem “Marmion: A Tale of Flodden Field” which is about a man romantically pursuing a woman by making up lies about her current fiancé and ultimately results in all their lives being changed for the worst.

If you lie, you have to consistently repeat that story to keep up the lie. This usually involves smaller lies to pad the bigger lie with so it blends in with truth. This is like a web, where all stories are connected and each must be upheld for the main big lie to be believable.

Someone who doesn’t have years of experience in lying and its consequences won’t know that each subsequent lie now needs to be upheld, so things get messy.