Most strategic games are about decisions, and when you decide to do something you’re also often deciding not to do something else. And there is a cost there, and that cost is often not appreciated by some designers.
— Tom Lehmann
Your game is 3 to 10 times harder than you think it is.
— Elizabeth Hargrave
To make a bridge to the familiar, hobby gamers have to realize what is familiar to a casual gamer.

Worker placement? nope
Variable turn order? nope
Variable set-up? not really
Deck construction? nope
Game phases? nope

You can ask a casual player to learn 2-3 new things at most
— Dominic Crapuchettes
A key facet of modern design is that players are engaged in the game from start to finish. Make losing as engaging as possible.
— T.C. Petty III
Hey you! You know that idea that you have for a new board game? The one you’ve been stewing over for some time now? Well...

GET UP AND GO MAKE IT!

Seriously! Grab some index cards, grab some pennies - whatever you need - and MAKE IT! You’ll thank me later.
— Tim Blank