The 'best before date' is not a conspiracy, but it is a source of confusion for many consumers. Many people seem to think, or at least to behave, as if the food in the container can somehow sense the expiry date, and turns rancid at 00:01 the next day.
I blame this form of magical thinking on mass entertainment like Star Trek: The Next Generation for this, when lethal radiation exposure or similar effect had this 'all or nothing' aspect. Typically the day was saved seconds before instant death, and a hypospray made everyone right as rain. (If only!)
The truth is more nuanced. For most foods labelled with 'best before' date are not 100% safe to eat beforehand, nor 100% unsafe after. In most cases, the best before date is simply a guide to freshness. The food will taste best and be most nutritious if consumed before the printed date, and will be less tasty and less nutritious afterward. Most sealed containers are still quite usable well past the best before date. If the seal has been broken, though, all bets are off. You need to rely on eye, smell, and taste tests to judge those, regardless of the date.
Of course, you can use the best before date to try and pick the freshest milk, eggs, bagged salad, etc. at your local grocer. They'd much rather you take the closer-to-expiry stuff, but no one's going to do that except maybe the zombie dads making the Sunday night emergency milk run.
I noted this at food drive, but it bears repeating: certain items have actual expiry dates, rather than best before dates. These items are unsafe to use once they have expired. The Canadian Food Inspection Agency provides this list (which I am quoting verbatim):