One thorn of experience is worth a whole wilderness of warning.
— James Russell Lowell

History is a vast early warning system.
Norman Cousins warning quote

I’m not saying it's wrong to plan for the future. I’m warning not to make today a victim of those plans.
— Steve Maraboli

In the US we find the label requirements are crazy. It is almost as if we had to label a bookcase with the warning 'do not eat this bookcase -- it can be harmful to your health'.
— Bjorn Bayley

If you must hold yourself up to your children as an object lesson, hold yourself up as a warning and not as an example.
— warning quotation by George Bernard Shaw