While not biologically correct, "the mind is a muscle" offers some merit, and it is true... "when you don't use it, you lose it." Think tank studies overwhelm us with evidence that memory is contingent upon attention and interest. To a certain extent we can, in fact, hold others accountable for the ability to remember.
On the flip side, however, the best of us can overwhelm, over-absorb, spread too thinly and/or burn out.
"I forgot" is not a legitimate excuse. To that end here is a quick organizational trick to ensuring top efficiency in daily priorities and task handling...
Use technology wisely. Use task reminders and event invitations. Require email correspondence as a paper trail to avoid confusion.
Create email folders and filters. Use subject lines, keywords and especially senders to automatically sort incoming and outgoing correspondence for quicker future reference. Use technology to automatically attach correspondence to contact records. Consider privacy protection for items of public sensitivity.
Use flags, priority codes and subject line keywords to set expectations of deadlines and urgency.
If you do not have someone on your team to help you with this, make it a priority to acquire someone, internally or externally to set this up. Give that priority a big red flag on your desktop of "to do's." For those who do not work at a desk, mobile desktops and PDAs are available.