• …how the average person opens their mail?
• …how a right-handed person accepts your business card when you hand it to her?
• …a left-handed person?
• …how many gatekeepers your portfolio mailer might have to go through before it gets in the decision-maker’s hands (and what they might or might not do to it)?
• …whether or not your envelope color allows the USPS to mark it and read it without difficulty?
• …what will happen if you ship a 5×7″ card of acrylic without padding?
• …when addressing envelopes with beautifully ornate script might be a bad thing?
• …what the environmental conditions are on USPS/UPS/DHL/FedEx airplanes? Or in the cargo-hold of passenger planes?
• …what you can learn about shipping invitations from museum curators and the way they crate art?
• …which is more permanent? Ink or graphite?
• …what to do when a guest sends back a blank RSVP card (with no return address)?
• …how to control the way someone experiences your product when you’re not there to guide them?
• …how humid it is in a place you’ve never visited?
• …if there’s a color blacker than black?
• …whiter than white?
• …how to Pantone match someone’s hair?
• …if it’s possible to make a self-filling helium balloon?
• …if your guests actually understand that only the names on the invitation are invited?
• …how your monogram will read painted on the side of a barn, in cut vinyl on panoramic windows, and as a gobo?
• …how much rain falls on a mailman on a rainy day?
• …how to send a diecut postcard without paying an irregular mail fee?
• …how a fountain pen/mechanical pencil/bic click/sharpie will write on a piece of paper?
• …how to stop someone in their tracks with a single piece of paper?
• …how much information someone is willing to put on a postcard (and how much more if it’s in an envelope)?

Have you thought about these things? I have.