You know, when the ones at the top go a little soft. I'll usually make a pack of digestives last a week or more as I end up waiting a couple of days between eating the top 3-4 to allow the next batch to soften up.
Opened biscuits taste better than ones you try and eat through the packet.

WTF is wrong with you OP?
I can't stand the soggy biscuit.
OP no! Stale soft biscuits are ming. That reminds me of a friend who shakes his fizzy drinks to remove all the carbon dioxide, he only drinks them flat. Both are worse than putting your toilet paper roll the wrong way round.