Whenever I start a new project with MySQL or MariaDB I am tempted to jump in and start creating my schema and tables with nothing more than a basic outline of the requirements. Often the justification I give myself is that the sooner I have something up and running, the better off I'll be, and besides, there will be plenty of time to sort things out later. Even when I am absolutely sure my ad-hoc schema is only for "development purposes" and will "never ever be used in production" it often is.
A lot of grief can be avoided if time is taken right at the start, before any tables are defined, to plan. This is big picture time and every stakeholder, from IT to the developers to management and even to marketing, needs to be involved. If for no other reason than to set expectations.
Right at the start, everyone involved in