Careful, it's heavy!

[William Gothberg]

Because they won't talk to me.

[William Gothberg]

Not at all. You don't have to lift something off the ground to work out its weight.

Handy to know in advance so you can bring the right tools, but you won't hurt yourself if it's heavier than you were told. You'd try to lift it and say "it's too heavy, lend me a sack barrow".

Then you're not very bright. I have no trouble pulling upwards on a box at my maximum comfortable ability, finding that the box remains on the ground, then deciding to get help lifting it. Why would you pull harder than is comfortable?

Without pain, the indicator you're damaging yourself.

Two people lifting one box is half the effort, obviously.

Those sayings are for dumb housewives. There's all sorts of shit about catching colds too, which have no scientific basis.