It is unprofessional to forget when you have an appointment.
Marnie is very busy with work and has an appointment with a vendor this afternoon.
Marnie wants to do well and get her work done.
Marnie sets a reminder on her phone for the meeting.
Marnie gets so wrapped up in her work that she forgets to go to the vendor meeting.
Marnie maintains a good relationship with the vendor and gets her work done.
The vendor is upset and their business relationship with Marnie sours.