If you were about to drive to the other end of the country but needed to get a new tyre for your car first you wouldn’t get up that very morning, take the wheel off (assuming you had no spare) and then try to drive to the tyre shop. I know I wouldn’t. Some would, I’m sure.
I say this because something similar happens with disturbing regularity – people ring up wanting some glass that either takes three days to arrive or is out of stock and they immediately panic “but the door/cupboard/etc is going out tomorrow” or even more preposterous “I’ve already taken the old glass out.”
There are two rules in work like this – “measure twice, cut once” and “don’t remove something until you’re sure you can put it, or something, back.” I can’t at the moment think of a more succinct way to phrase the latter one to make it more snappy – as things have to be these days, inevitably.
Again it’s another example of the expectation, instilled into us now, that we should not expect to wait for anything, which as I’ve said before can snowball as one person promises something to be ready tomorrow and expects everyone else to fall in line. And in that lies a third lesson “don’t assume anything” especially regarding delivery times.